Electrophotographic photosensitive member, process cartridge, and image forming apparatus

ABSTRACT

An electrophotographic photosensitive member includes a conductive substrate and a single-layer photosensitive layer. The photosensitive layer contains a charge generating material, a hole transport material, an electron transport material, an additive, and a binder resin. An optical response time is in a range from 0.05 milliseconds to 0.85 milliseconds. The optical response time is a time from irradiation of a surface of the photosensitive layer charged to +800 V with pulse light having a wavelength of 780 nm to surface potential decay of the photosensitive layer from +800 V to +400 V. An optical intensity of the pulse light is set so that the surface potential of the photosensitive layer becomes +200 V from +800 V after 400 milliseconds from pulse light irradiation of the surface of the photosensitive layer charged to the +800 V. The additive includes either of both an ultraviolet absorbing agent and an antioxidant.

INCORPORATION BY REFERENCE

The present application claims priority under 35 U.S.C. § 119 to Japanese Patent Application No. 2018-014335, filed on Jan. 31, 2018. The contents of this application are incorporated herein by reference in their entirety.

BACKGROUND

The present disclosure relates to an electrophotographic photosensitive member, a process cartridge, and an image forming apparatus.

Electrophotographic photosensitive members are used in electrographic image forming apparatuses. For example, a multi-layer electrophotographic photosensitive member or a single-layer electrophotographic photosensitive member is used as an electrophotographic photosensitive member. The electrophotographic photosensitive member includes a photosensitive layer. The multi-layer electrophotographic photosensitive member includes, as the photosensitive layer, a charge generating layer having a charge generating function and a charge transport layer having a charge transporting function. The single-layer electrophotographic photosensitive member includes, as the photosensitive layer, a photosensitive layer that is a single layer having the charge generating function and the charge transporting function.

An example of the electrophotographic photosensitive member is disclosed as a photosensitive member capable of inhibiting image ghost with a photosensitive layer covered with a protective layer containing a curing resin and a specific charge transport material.

SUMMARY

An electrophotographic photosensitive member according to an aspect of the present disclosure includes a conductive substrate and a photosensitive layer of a single layer. The photosensitive layer contains a charge generating material, a hole transport material, an electron transport material, an additive, and a binder resin. An optical response time is at least 0.05 milliseconds and no greater than 0.85 milliseconds. The optical response time is a time from irradiation to decay. The irradiation is a time of a start of irradiation of a surface of the photosensitive layer charged to +800 V with pulse light having a wavelength of 780 nm. The decay is a time when a surface potential of the photosensitive layer decays from +800 V to +400 V. An optical intensity of the pulse light is set so that the surface potential of the photosensitive layer becomes +200 V from +800 V when 400 milliseconds elapse after the irradiation of the surface of the photosensitive layer charged to +800 V with the pulse light. The additive includes at least one of an ultraviolet absorbing agent and an antioxidant.

A process cartridge according to the present disclosure includes the electrophotographic photosensitive member described above.

An image forming apparatus according to an aspect of the present disclosure includes an image bearing member, a charger, a light exposure section, a developing section, and a transfer section. The charger charges a surface of the image bearing member. The light exposure section exposes the charged surface of the image bearing member to light to form an electrostatic latent image on the surface of the image bearing member. The developing section develops the electrostatic latent image into a toner image. The transfer section transfers the toner image from the image bearing member to a transfer target. The charger positively charges the surface of the image bearing member. The image bearing member is the electrophotographic photosensitive member described above.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a partial cross-sectional view illustrating an example of an electrophotographic photosensitive member according to a first embodiment of the present disclosure.

FIG. 1B is a partial cross-sectional view illustrating another example of the electrophotographic photosensitive member according to the first embodiment of the present disclosure.

FIG. 2 is a graph representation showing a surface potential decay curve of a photosensitive layer.

FIG. 3 is a diagram illustrating an example of an image forming apparatus according to a second embodiment of the present disclosure.

FIG. 4 is a diagram illustrating an optical response time measuring apparatus.

FIG. 5 is a diagram illustrating an evaluation image.

FIG. 6 is a diagram illustrating an image with an image defect resulting from exposure memory.

DETAILED DESCRIPTION

Hereinafter, embodiments of the present disclosure will be described. The present disclosure is not in any way limited by the following embodiments. The present disclosure can be practiced within a scope of objects of the present disclosure with alterations made as appropriate. Although some overlapping explanations may be omitted as appropriate, such omission does not limit the gist of the present disclosure.

In the following description, the term “-based” may be appended to the name of a chemical compound to form a generic name encompassing both the chemical compound itself and derivatives thereof. When the term “-based” is appended to the name of a chemical compound used in the name of a polymer, the term indicates that a repeating unit of the polymer originates from the chemical compound or a derivative thereof.

Hereinafter, the following definitions apply to a halogen atom, an alkyl group having a carbon number of at least 10 and no greater than 30, an alkyl group having a carbon number of at least 15 and no greater than 25, an alkyl group having a carbon number of at least 1 and no greater than 10, an alkyl group having a carbon number of at least 1 and no greater than 8, an alkyl group having a carbon number of at least 1 and no greater than 6, an alkyl group having a carbon number of at least 1 and no greater than 5, an alkyl group having a carbon number of at least 1 and no greater than 4, an alkyl group having a carbon number of at least 1 and no greater than 3, an alkyl group having a carbon number of 1, 4, or 8, an alkyl group having a carbon number of at least 3 and no greater than 10, an alkyl group having a carbon number of at least 3 and no greater than 5, an alkenyl group having a carbon number of at least 2 and no greater than 4, an alkoxy group having a carbon number of at least 1 and no greater than 6, an alkoxy group having a carbon number of at least 1 and no greater than 3, an aryl group having a carbon number of at least 6 and no greater than 14, an aryl group having a carbon number of at least 6 and no greater than 10, an aralkyl group having a carbon number of at least 7 and no greater than 20, an aralkyl group having a carbon number of at least 7 and no greater than 16, a heterocyclic group, and a cycloalkane having a carbon number of at least 5 and no greater than 7, unless otherwise stated.

Examples of halogen atoms include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom.

The alkyl group having a carbon number of at least 10 and no greater than 30 and the alkyl group having a carbon number of at least 15 and no greater than 25 each are an unsubstituted straight chain or branched chain alkyl group. Examples of alkyl groups having a carbon number of at least 10 and no greater than 30 include dodecyl group, tridecyl group, tetradecyl group, pentadecyl group, hexadecyl group, heptadecyl group, octadecyl group, nonadecyl group, and eicosyl group. Examples of alkyl groups having a carbon number of at least 15 and no greater than 25 are the groups having a carbon number of at least 15 and no greater than 25 among the above-listed examples of alkyl groups having a carbon number of at least 10 and no greater than 30.

The alkyl group having a carbon number of at least 1 and no greater than 10, the alkyl group having a carbon number of at least 1 and no greater than 8, the alkyl group having a carbon number of at least 1 and no greater than 6, the alkyl group having a carbon number of at least 1 and no greater than 5, the alkyl group having a carbon number of at least 1 and no greater than 4, the alkyl group having a carbon number of at least 1 and no greater than 3, the alkyl group having a carbon number of 1, 4, or 8, the alkyl group having a carbon number of at least 3 and no greater than 10, and the alkyl group having a carbon number of at least 3 and no greater than 5 each are an unsubstituted straight chain or branched chain alkyl group. Examples of alkyl groups having a carbon number of at least 1 and no greater than 10 include methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, sec-butyl group, tert-butyl group, pentyl group, isopentyl group, 1,1-dimethylpropyl group, neopentyl group, hexyl group, heptyl group, and octyl group. Examples of alkyl groups having a carbon number of at least 1 and no greater than 8 are the groups having a carbon number of at least 1 and no greater than 8 among the above-listed examples of alkyl groups having a carbon number of at least 1 and no greater than 10. Examples of alkyl groups having a carbon number of at least 1 and no greater than 6 are the groups having a carbon number of at least 1 and no greater than 6 among the above-listed examples of alkyl groups having a carbon number of at least 1 and no greater than 10. Examples of alkyl groups having a carbon number of at least 1 and no greater than 5 are the groups having a carbon number of at least 1 and no greater than 5 among the above-listed examples of alkyl groups having a carbon number of at least 1 and no greater than 10. Examples of alkyl groups having a carbon number of at least 1 and no greater than 4 are the groups having a carbon number of at least 1 and no greater than 4 among the above-listed examples of alkyl groups having a carbon number of at least 1 and no greater than 10. Examples of alkyl groups having a carbon number of at least 1 and no greater than 3 are the groups having a carbon number of at least 1 and no greater than 3 among the above-listed examples of alkyl groups having a carbon number of at least 1 and no greater than 10. Examples of alkyl groups having a carbon number of 1, 4, or 8 are the groups having a carbon number of 1, 4, or 8 among the above-listed examples of alkyl groups having a carbon number of at least 1 and no greater than 10. Examples of alkyl groups having a carbon number of at least 3 and no greater than 10 are the groups having a carbon number of at least 3 and no greater than 10 among the above-listed examples of alkyl groups having a carbon number of at least 1 and no greater than 10. Examples of alkyl groups having a carbon number of at least 3 and no greater than 5 are the groups having a carbon number of at least 3 and no greater than 5 among the above-listed examples of alkyl groups having a carbon number of at least land no greater than 10.

The alkenyl group having a carbon number of at least 2 and no greater than 4 is an unsaturated straight chain or branched chain alkenyl group. The alkenyl group having a carbon number of at least 2 and no greater than 4 has one or two double bonds. Examples of alkenyl groups having a carbon number of at least 2 and no greater than 4 include ethenyl group, propenyl group, butenyl group, and butadienyl group.

The alkoxy group having a carbon number of at least 1 and no greater than 6 and the alkoxy group having a carbon number of at least 1 and no greater than 3 each are an unsubstituted straight chain or branched chain alkoxy group. Examples of alkoxy groups having a carbon number of at least 1 and no greater than 6 include methoxy group, ethoxy group, n-propoxy group, isopropoxy group, n-butoxy group, sec-butoxy group, tert-butoxy group, pentyloxy group, isopentyloxy group, neopentyloxy group, and hexyloxy group. Examples of alkoxy groups having a carbon number of at least 1 and no greater than 3 are the groups having a carbon number of at least 1 and no greater than 3 among the above-listed examples of alkoxy groups having a carbon number of at least 1 and no greater than 6.

The aryl group having a carbon number of at least 6 and no greater than 14 and the aryl group having a carbon number of at least 6 and no greater than 10 each are an unsubstituted aryl group. Examples of aryl groups having a carbon number of at least 6 and no greater than 14 include phenyl group, naphthyl group, indacenyl group, biphenylenyl group, acenaphthylenyl group, anthryl group, and phenanthryl group. Examples of aryl groups having a carbon number of at least 6 and no greater than 10 include phenyl group and naphthyl group.

The aralkyl group having a carbon number of at least 7 and no greater than 20 and the aralkyl group having a carbon number of at least 7 and no greater than 16 each are an unsubstituted aralkyl group. Examples of aralkyl groups having a carbon number of at least 7 and no greater than 20 include an alkyl group having a carbon number of at least 1 and no greater than 6 and substituted by an aryl group having a carbon number of at least 6 and no greater than 14. Examples of aralkyl groups having a carbon number of at least 7 and no greater than 16 include an alkyl group having a carbon number of 1 or 2 and substituted by an aryl group having a carbon number of at least 6 and no greater than 14.

Examples of heterocyclic groups include a heterocyclic group having at least 5 members and no greater than 14 members. The heterocyclic group having at least 5 members and no greater than 14 members is an unsubstituted heterocyclic group having at least 1 hetero atom in addition to carbon atoms. The hetero atom is at least one atom selected from the group consisting of a nitrogen atom, a sulfur atom, and an oxygen atom. Examples of heterocyclic groups having at least 5 members and no greater than 14 members include: a heterocyclic group having a five- or six-membered monocyclic heterocyclic ring having at least 1 and no greater than 3 hetero atoms in addition to carbon atoms (also referred to below as a heterocyclic ring (H)); a heterocyclic group formed through condensation of two heterocyclic rings (H); a heterocyclic group formed through condensation of a heterocyclic ring (H) and a five- or six-membered monocyclic hydrocarbon ring; a heterocyclic group formed through condensation of three heterocyclic rings (H); a heterocyclic group formed through condensation of two heterocyclic rings (H) and one five- or six-membered monocyclic hydrocarbon ring; and a heterocyclic group formed through condensation of one heterocyclic ring (H) and two five- or six-membered monocyclic hydrocarbon rings. Specific examples of heterocyclic groups having at least 5 members and no greater than 14 members include piperidinyl group, piperazinyl group, morpholinyl group, thiophenyl group, furanyl group, pyrrolyl group, imidazolyl group, pyrazolyl group, isothiazolyl group, isoxazolyl group, oxazolyl group, thiazolyl group, furazanyl group, pyranyl group, pyridyl group, pyridazinyl group, pyrimidinyl group, pyrazinyl group, indolyl group, 1H-indazolyl group, isoindolyl group, chromenyl group, quinolinyl group, isoquinolinyl group, purinyl group, pteridinyl group, triazolyl group, tetrazolyl group, 4H-quinolizinyl group, naphthyridinyl group, benzofuranyl group, 1,3-benzodioxolyl group, benzoxazolyl group, benzothiazolyl group, benzimidazolyl group, carbazolyl group, phenanthridinyl group, acridinyl group, phenadinyl group, and phenanthrolinyl group.

The cycloalkane having a carbon number of at least 5 and no greater than 7 is an unsubstituted cycloalkane. Examples of cycloalkanes having a carbon number of at least 5 and no greater than 7 include cyclopentane, cyclohexane, and cycloheptane.

First Embodiment: Electrophotographic Photosensitive Member

A first embodiment relates to an electrophotographic photosensitive member (also referred to below as a photosensitive member). The following describes structure of a photosensitive member 1 with reference to FIGS. 1A and 1B. FIGS. 1A and 1B are cross-sectional views each illustrating an example of the photosensitive member 1 according to the first embodiment.

As illustrated in FIG. 1A, the photosensitive member 1 includes for example a conductive substrate 2 and a photosensitive layer 3. The photosensitive layer 3 is a single layer (one layer). The photosensitive member 1 is a single-layer electrophotographic photosensitive member including the photosensitive layer 3 of a single layer.

As illustrated in FIG. 1B, the photosensitive member 1 may include an intermediate layer 4 (undercoat layer) in addition to the conductive substrate 2 and the photosensitive layer 3. The intermediate layer 4 is disposed between the conductive substrate 2 and the photosensitive layer 3. The photosensitive layer 3 may be disposed directly on the conductive substrate 2 as illustrated in FIG. 1A. Alternatively, the photosensitive layer 3 may be disposed on the conductive substrate 2 with the intermediate layer 4 therebetween as illustrated in FIG. 1B. The intermediate layer 4 may include one layer or a plurality of layers.

The photosensitive member 1 may further include a protective layer (not illustrated) in addition to the conductive substrate 2 and the photosensitive layer 3. The protective layer is disposed on the photosensitive layer 3. The protective layer may include one layer or a plurality of layers.

The thickness of the photosensitive layer 3 is not particularly limited. The photosensitive layer 3 preferably has a thickness of at least 5 μm and no greater than 100 μm, and more preferably at least 10 μm and no greater than 50 μm. The structure of the photosensitive member 1 has been described with reference to FIGS. 1A and 1B. The following describes the photosensitive member further in detail.

<Photosensitive Layer>

The photosensitive layer contains a charge generating material, a hole transport material, an electron transport material, an additive, and a binder resin.

(Optical Response Time)

An optical response time of the photosensitive member is at least 0.05 milliseconds and no greater than 0.85 milliseconds. The optical response time is a time from a time of a start of irradiation of a surface of the photosensitive layer charged to +800 V with pulse light having a wavelength of 780 nm to a time when a surface potential of the photosensitive layer decays from +800 V to +400 V. An optical intensity of the pulse light is set so that the surface potential of the photosensitive layer becomes +200 V from +800 V when 400 milliseconds elapse after irradiation of the surface of the photosensitive layer charged to +800 V with the pulse light having a wavelength of 780 nm.

The following describes the optical response time with reference to FIG. 2. FIG. 2 is a graph representation showing a surface potential decay curve of a photosensitive layer. A vertical axis of the graph representation represents surface potential (unit: V) of the photosensitive layer. A horizontal axis represents elapse of time. On the surface potential decay curve of the photosensitive layer, a time point when the surface of the photosensitive layer is irradiated with the pulse light (more precisely, a time point when output of the pulse light with which the surface of the photosensitive layer is irradiated exhibits peak output) is determined to be 0.00 milliseconds. As shown by the surface potential decay curve of the photosensitive layer, the surface potential of the photosensitive layer decays from +800 V to +200 V when 400 milliseconds elapse after irradiation of the surface of the photosensitive layer charged to +800 V with the pulse light. Here, a time τ from a time of a start of irradiation of the surface of the photosensitive layer charged to +800 V with the pulse light to a time when the surface potential of the photosensitive layer decays from +800 V to +400 V is taken to be an optical response time.

When the optical response time of the photosensitive member is at least 0.05 milliseconds and no greater than 0.85 milliseconds, an image defect resulting from exposure memory can be inhibited and excellent potential stability can be achieved. The exposure memory herein means a phenomenon in which influence of light exposure in image formation causes charge potential of a surface region of a photosensitive member in the current turn corresponding to an exposure region thereof in the previous turn to be lower than charge potential of a surface region of the photosensitive member corresponding to a non-exposure region in the previous turn. When exposure memory occurs, an image defect described as a darken region corresponding to the exposure region of the photosensitive member in the previous turn occurs in a formed image. When the optical response time of the photosensitive member exceeds 0.85 milliseconds, electrical charge (particularly, holes) tends to remain in the photosensitive layer. Accordingly, an image defect resulting from exposure memory may occur to impair potential stability. Note that it takes some time for the photosensitive member to make optical response, and therefore, a lower limit of the optical response time of the photosensitive member may be 0.05 milliseconds.

In order to further efficiently prevent induction of an image defect resulting from exposure memory, an upper limit of the optical response time of the photosensitive member is preferably 0.60 milliseconds, more preferably 0.45 milliseconds, and further preferably 0.40 milliseconds.

The optical response time of the photosensitive member is measured by a method described in Examples. The optical response time of the photosensitive member can be adjusted for example by changing a type of the hole transport material. The optical response time of the photosensitive member can be also adjusted for example by changing a type of the electron transport material. The optical response time of the photosensitive member can be also adjusted for example by changing a type of the additive. Furthermore, the optical response time of the photosensitive member can be adjusted for example by changing a content of the hole transport material relative to a mass of the photosensitive layer. In addition, the optical response time of the photosensitive member can be adjusted for example by changing a ratio m_(HTM)/m_(ETM) of a mass m_(HTM) of the hole transport material to a mass m_(ETM) of the electron transport material.

(Additive)

The additive includes at least one of an ultraviolet absorbing agent and an antioxidant. As a result of the additive including at least one of an ultraviolet absorbing agent and an antioxidant, potential stability of the photosensitive member can be improved. Presumably, the reason therefor is as follows. The hole transport material and the like contained in the photosensitive member may vary in property due to ultraviolet rays included in light to which the photosensitive member is exposed in production or replacement of the photosensitive member or ultraviolet rays included in light leaking in through a casing of the image forming apparatus in use. By contrast, inclusion of an ultraviolet absorbing agent as the additive in the photosensitive member can inhibit variation in property of the hole transport material and the like caused by ultraviolet rays, resulting in improvement in potential stability of the photosensitive member. Furthermore, when radicals are generated in the photosensitive layer, charge transport in the photosensitive layer is inhibited by the radicals to cause residual charges. This makes it difficult to charge the surface of the photosensitive member. In view of the foregoing, the photosensitive layer contains an antioxidant as the additive, with a result that radicals generated in the photosensitive layer can be scavenged. As a result, residual charges caused due to the presence of radicals in the photosensitive layer decrease to improve potential stability of the photosensitive member.

Examples of ultraviolet absorbing agents include benzotriazole-based ultraviolet absorbing agents, triazine-based ultraviolet absorbing agents, and benzophenone-based ultraviolet absorbing agents. The benzotriazole-based ultraviolet absorbing agents, the triazine-based ultraviolet absorbing agents, and the benzophenone-based ultraviolet absorbing agents are respectively ultraviolet absorbing agents having benzotriazole structure, ultraviolet absorbing agents having triazine structure, and ultraviolet absorbing agents having benzophenone structure. In order to further improve potential stability of the photosensitive member, the additive preferably includes a benzotriazole-based ultraviolet absorbing agent. The benzotriazole-based ultraviolet absorbing agent preferably includes a compound represented by general formula (1) shown below (also referred to below as a compound (1)). The photosensitive layer may contain only one ultraviolet absorbing agent or two or more ultraviolet absorbing agents.

In general formula (1), R¹ represents a halogen atom or an alkyl group having a carbon number of at least 1 and no greater than 6 and substituted by a halogen atom. R² represents an alkyl group having a carbon number of at least 1 and no greater than 10, an aralkyl group having a carbon number of at least 7 and no greater than 20, or an aryl group having a carbon number of at least 6 and no greater than 22. Also, n and m each represent, independently of each other, an integer of at least 0 and no greater than 4. When n represents an integer of at least 2 and no greater than 4, plural chemical groups R¹ may be the same as or different from one another. When m represents an integer of at least 2 and no greater than 4, plural chemical groups R² may be the same as or different from one another.

In general formula (1), the alkyl group having a carbon number of at least 1 and no greater than 6 and substituted by a halogen atom and represented by R¹ is preferably an alkyl group having a carbon number of at least 1 and no greater than 3 and substituted by a halogen atom, and more preferably an alkyl group having a carbon number of at least 1 and no greater than 3 and substituted by a chlorine atom. The halogen atom represented by R¹ is preferably a fluorine atom or a chlorine atom, and more preferably a chlorine atom. Preferably, R¹ in general formula (1) represents a halogen atom.

In general formula (1), the alkyl group having a carbon number of at least 1 and no greater than 10 represented by R² is preferably an alkyl group having a carbon number of at least 1 and no greater than 8, more preferably an alkyl group having a carbon number of at least 1, 4, or 8, and further preferably a methyl group, a tert-butyl group, or a tert-octyl group. The aralkyl group having a carbon number of at least 7 and no greater than 20 represented by R² is preferably an aralkyl group having a carbon number of at least 7 and no greater than 16. The aryl group having a carbon number of at least 6 and no greater than 22 represented by R² is preferably an aryl group having a carbon number of at least 6 and no greater than 14. Preferably, R² in general formula (1) represents an alkyl group having a carbon number of at least 1 and no greater than 10.

In general formula (1), it is preferable that n represents 0 or 1 and m represents 1 or 2.

Preferably, the compound (1) is a compound represented by chemical formula (AD1) or (AD2) shown below (also referred to below as compounds (AD1) and (AD2)). In the chemical formula (AD1), t-C₄H₉ represents a tert-butyl group.

Examples of antioxidants include hindered phenol-based antioxidants, hindered amine-based antioxidants, sulfur-based antioxidants, and phosphorous-based antioxidants. The hindered phenol-based antioxidants, the hindered amine-based antioxidants, the sulfur-based antioxidants, and the phosphorus-based antioxidants are respectively antioxidants having hindered phenol structure, antioxidants having hindered amine structure, antioxidants having sulfur atoms, and antioxidants having phosphorous atoms. In order to further improve potential stability of the photosensitive member, the additive preferably includes a hindered phenol-based antioxidant. The hindered phenol-based antioxidant preferably includes a compound represented by general formula (2A) or (2B) shown below (also referred to below as a compound (2A) and (2B)). The photosensitive layer may include only one antioxidant or two or more antioxidants.

In general formulas (2A) and (2B), R³ and R⁵ each represent, independently of each other, an alkyl group having a carbon number of at least 3 and no greater than 10. R⁴ represents a chemical group obtained through elimination of s hydrogen atom(s) from an alkane having a carbon number of at least 1 and no greater than 3. Z represents a hydrogen atom, an alkyl group having a carbon number of at least 1 and no greater than 4, or a monovalent group represented by general formula (Z) shown below. Furthermore, p and t each represent, independently of each other, an integer of at least 1 and no greater than 4. Also, q and r each represent, independently of each other, an integer of at least 1 and no greater than 3. Also, s represents an integer of at least 1 and no greater than 4. When at least one of p and s represents an integer of at least 2 and no greater than 4, the plural chemical groups R³ may be the same as or different from one another. When s represents an integer of at least 2 and no greater than 4, plural integers p may be the same as or different from one another, plural integers q may be the same as or different from one another, and plural integers r may be the same as or different from one another. When t represents an integer of at least 2 and no greater than 4, plural chemical groups R⁵ may be the same as or different from one another.

In general formula (Z), R⁶ represents an alkyl group having a carbon number of at least 10 and no greater than 30. Furthermore, u represents an integer of at least 1 and no greater than 3.

In general formulas (2A) and (2B), R³ and R⁵ preferably each represent, independently of each other, an alkyl group having a carbon number of at least 3 and no greater than 10, more preferably an alkyl group having a carbon number of at least 3 and no greater than 5, further preferably a branched alkyl group having a carbon number of at least 3 and no greater than 5, and particularly preferably a tert-butyl group. In general formula (2A), the chemical group represented by R⁴ is an alkyl group having a carbon number of at least 1 and no greater than 3 when s represents 1, an alkanediyl group having a carbon number of at least 1 and no greater than 3 when s represents 2, an alkanetriyl group having a carbon number of at least 1 and no greater than 3 when s represents 3, and an alkanetetrayl group having a carbon number of at least 1 and no greater than 3 when s represents 4, for example. Preferably, R⁴ represents a chemical group obtained through elimination of s hydrogen atom(s) from a methyl group. That is, it is preferable that R⁴ represents a methyl group when s represents 1, a methanediyl group when s represents 2, a methanetriyl group when s represents 3, and a methanetetrayl group when s represents 4.

In general formula (2B), Z preferably represents a methyl group or a monovalent group represented by general formula (Z).

In general formulas (2A) and (2B), p and t preferably each represent an integer of at least 1 and no greater than 3, and more preferably 2.

In general formula (2A), q preferably represents 2. Preferably, r represents 1. Preferably, s represents 4.

In general formula (Z), u preferably represents 2. R⁶ more preferably represents an alkyl group having a carbon number of at least 15 and no greater than 25, and further preferably an octadecyl group.

The hindered phenol-based antioxidant preferably includes at least one of compounds represented by chemical formulas (AD3), (AD4), and (AD5) shown below. In the following description, the compounds represented by chemical formulas (AD3), (AD4), and (AD5) may be referred to as compounds (AD3), (AD4), and (AD5), respectively.

The photosensitive layer may contain as the additive either or both one or more ultraviolet absorbing agent and one or more antioxidant (for example, two compounds (AD1) and (AD3)).

In order to improve potential stability of the photosensitive member, a total amount of the ultraviolet absorbing agent and the antioxidant is preferably at least 0.1 parts by mass relative to 100 parts by mass of the binder resin, more preferably at least 0.5 parts by mass, and further preferably at least 3 parts by mass. In order to improve potential stability of the photosensitive member, the total amount of the ultraviolet absorbing agent and the antioxidant is preferably no greater than 15 parts by mass relative to 100 parts by mass of the binder resin, more preferably no greater than 10 parts by mass, and further preferably no greater than 7 parts by mass.

In order to improve potential stability of the photosensitive member, a total content of the ultraviolet absorbing agent and the antioxidant is preferably at least 0.2% by mass relative to a mass of the photosensitive layer, and more preferably at least 1.0% by mass. In order to improve potential stability of the photosensitive member, the total content of the ultraviolet absorbing agent and the antioxidant is preferably no greater than 7% by mass relative to the mass of the photosensitive layer, and more preferably no greater than 3% by mass.

The photosensitive layer may further contain another additive (also referred to below as an additional additive) as the additive in addition to at least one of the ultraviolet absorbing agent and the antioxidant. Examples of additional additives include softeners, surface modifiers, extenders, thickeners, dispersion stabilizers, waxes, acceptors, donors, surfactants, plasticizers, sensitizers, and leveling agents.

(Hole Transport Material)

Examples of hole transport materials include triphenylamine derivatives, diamine derivatives (for example, N,N,N′,N′-tetraphenylbenzidine derivative, N,N,N′,N′-tetraphenylphenylenediamine derivative, N,N,N′,N′-tetraphenylnaphtylenediamine derivative, N,N,N′,N′-tetraphenylphenanthrylenediamine derivative, and di(aminophenylethenyl) benzene derivative), oxadiazole-based compounds (for example, 2,5-di(4-methylaminophenyl)-1,3,4-oxadiazole), styryl-based compounds (for example, 9-(4-diethylaminostyryl)anthracene), carbazole-based compounds (for example, polyvinyl carbazole), organic polysilane compounds, pyrazoline-based compounds (for example, 1-phenyl-3-(p-dimethylaminophenyl)pyrazoline), hydrazone-based compounds, indole-based compounds, oxazole-based compounds, isoxazole-based compounds, thiazole-based compounds, thiadiazole-based compounds, imidazole-based compounds, pyrazole-based compounds, and triazole-based compounds. The photosensitive layer may contain only one hole transport material or two or more hole transport materials.

In order to effectively inhibit an image defect resulting from exposure memory, the hole transport material preferably includes at least one of compounds represented by general formulas (11) to (18) shown below. In the following description, the compounds represented by general formulas (11) to (18) may be referred to as compounds (11) to (18), respectively.

The following describes the compound (11). In general formula (11), Q¹, Q², Q³, and Q⁴ each represent, independently of one another, an alkyl group having a carbon number of at least 1 and no greater than 6. Furthermore, b₁, b₂, b₃, and b₄ each represent, independently of one another, an integer of at least 0 and no greater than 5. Also, b₅ represents 0 or 1.

When b₁ represents an integer of at least 2 and no greater than 5, plural chemical groups Q¹ may be the same as or different from one another. When b₂ represents an integer of at least 2 and no greater than 5, plural chemical groups Q² may be the same as or different from one another. When b₃ represents an integer of at least 2 and no greater than 5, plural chemical groups Q³ may be the same as or different from one another. When b₄ represents an integer of at least 2 and no greater than 5, plural chemical groups Q₄ may be the same as or different from one another.

In general formula (11), the alkyl group having a carbon number of at least 1 and no greater than 6 represented by any of Q¹, Q², Q³, and Q⁴ is preferably an alkyl group having a carbon number of at least 1 and no greater than 3, and more preferably a methyl group.

In general formula (11), Q¹, Q², Q³, and Q⁴ preferably each represent, independently of one another, an alkyl group having a carbon number of at least 1 and no greater than 3. Preferably, b₁, b₂, b₃, and b₄ each represent, independently of one another, 0 or 1.

Preferable examples of the compound (11) include compounds represented by chemical formulas (11-HT8) and (11-HT9) shown below (also referred to below as compounds (11-HT8) and (11-HT9), respectively).

The following describes the compound (12). In general formula (12), Q²¹ and Q²⁸ each represent, independently of each other, a hydrogen atom, a phenyl group optionally substituted by an alkyl group having a carbon number of at least 1 and no greater than 6, an alkyl group having a carbon number of at least 1 and no greater than 6, or an alkoxy group having a carbon number of at least 1 and no greater than 6. Q²² and Q²⁹ each represent, independently of each other, a phenyl group, an alkyl group having a carbon number of at least 1 and no greater than 6, or an alkoxy group having a carbon number of at least 1 and no greater than 6. Q²³, Q²⁴, Q²⁵, Q²⁶, and Q²⁷ each represent, independently of one another, a hydrogen atom, a phenyl group, an alkyl group having a carbon number of at least 1 and no greater than 6, or an alkoxy group having a carbon number of at least 1 and no greater than 6. Adjacent two of Q²³, Q²⁴, Q²⁵, Q²⁶, and Q²⁷ may be bonded together to form a ring (for example, a cycloalkane having a carbon number of at least 5 and no greater than 7, specific examples include cyclopentane, cyclohexane, and cycloheptane). Furthermore, d₁ and d₂ each represent, independently of each other, an integer of at least 0 and no greater than 2. Also, d₃ and d₄ each represent, independently of each other, an integer of at least 0 and no greater than 5.

When d₃ represents an integer of at least 2 and no greater than 5, plural chemical groups Q²² may be the same as or different from one another. When d₄ represents an integer of at least 2 and no greater than 5, plural chemical groups Q²⁹ may be the same as or different from one another.

In general formula (12), Q²¹ and Q²⁸ preferably each represent, independently of each other, a hydrogen atom or a phenyl group optionally substituted by an alkyl group having a carbon number of at least 1 and no greater than 6. Q²² and Q²⁹ preferably each represent, independently of each other, an alkyl group having a carbon number of at least 1 and no greater than 6. Q²³, Q²⁴, Q²⁵, Q²⁶, and Q²⁷ preferably each represent, independently of one another, a hydrogen atom, an alkyl group having a carbon number of at least 1 and no greater than 6, or an alkoxy group having a carbon number of at least 1 and no greater than 6. Adjacent two of Q²³, Q²⁴, Q²⁵, Q²⁶, and Q²⁷ may be bonded together to form a cycloalkane having a carbon number of at least 5 and no greater than 7. In the above case, a condensation portion between a phenyl group and the cycloalkane having a carbon number of at least 5 and no greater than 7 may have a double bond. Preferably, d₁ and d₂ each represent, independently of each other, an integer of at least 0 and no greater than 2. Preferably, d₃ and d₄ each represent, independently of each other, 0 or 1.

The phenyl group optionally substituted by an alkyl group having a carbon number of at least 1 and no greater than 6 represented by Q²¹ or Q²⁸ is preferably a phenyl group optionally substituted by an alkyl group having a carbon number of at least 1 and no greater than 3, and more preferably a phenyl group optionally substituted by a methyl group. The alkyl group having a carbon number of at least 1 and no greater than 6 represented by Q²² or Q²⁹ is preferably an alkyl group having a carbon number of at least 1 and no greater than 3, and more preferably a methyl group. The alkyl group having a carbon number of at least 1 and no greater than 6 represented by any of Q²³, Q²⁴, Q²⁵, Q²⁶, and Q²⁷ is preferably an alkyl group having a carbon number of at least 1 and no greater than 4, more preferably a methyl group, an ethyl group, or an n-butyl group, and further preferably a methyl group. The alkoxy group having a carbon number of at least 1 and no greater than 6 represented by any of Q²³, Q²⁴, Q²⁵, Q²⁶, and Q²⁷ is preferably an alkoxy group having a carbon number of at least 1 and no greater than 3, and more preferably an ethoxy group. Cyclohexane is preferable as the cycloalkane having a carbon number of at least 5 and no greater than 7 and formed by adjacent two of Q²³, Q²⁴, Q²⁵, Q²⁶, and Q²⁷ bonded together.

In general formula (12), it is preferable that Q²¹ and Q²⁸ are the same as each other, Q²² and Q²⁹ are the same as each other, d₁ and d₂ represent the same integer, and d₃ and d₄ represent the same integer.

Preferable examples of the compound (12) include compounds represented by chemical formulas (12-HT3), (12-HT4), (12-HT5), (12-HT6), (12-HT10), (12-HT11), (12-HT12), and (12-HT18) shown below (also referred to below as compounds (12-HT3), (12-HT4), (12-HT5), (12-HT6), (12-HT10), (12-HT11), (12-HT12), and (12-HT18), respectively).

The following describes the compound (13). In general formula (13), Q³¹, Q³², Q³³, and Q³⁴ each represent, independently of one another, an alkyl group having a carbon number of at least 1 and no greater than 6 or an alkoxy group having a carbon number of at least 1 and no greater than 6. Furthermore, e₁, e₂, e₃, and e₄ each represent, independently of one another, an integer of at least 0 and no greater than 5. Also, e₅ represents 2 or 3.

When e₁ represents an integer of at least 2 and no greater than 5, plural chemical groups Q³¹ may be the same as or different from one another. When e₂ represents an integer of at least 2 and no greater than 5, plural chemical groups Q³² may be the same as or different from one another. When e₃ represents an integer of at least 2 and no greater than 5, plural chemical groups Q³³ may be the same as or different from one another. When e₄ represents an integer of at least 2 and no greater than 5, plural chemical groups Q³⁴ may be the same as or different from one another.

In general formula (13), Q³¹, Q³², Q³³, and Q³⁴ preferably each represent, independently of one another, an alkyl group having a carbon number of at least 1 and no greater than 6. The alkyl group having a carbon number of at least 1 and no greater than 6 represented by any of Q³¹, Q³², Q³³, and Q³⁴ is preferably an alkyl group having a carbon number of at least 1 and no greater than 3, and more preferably a methyl group. Preferably, e₁, e₂, e₃, and e₄ each represent, independently of one another, 0 or 1. Preferably, e₅ represents 2 or 3.

Preferable examples of the compound (13) include compounds represented by chemical formulas (13-HT16) and (13-HT17) shown below (also referred to below as compounds (13-HT16) and (13-HT17), respectively).

The following describes the compound (14). In general formula (14), Q⁴¹, Q⁴², Q⁴³, Q⁴⁴, Q⁴⁵, and Q⁴⁶ each represent, independently of one another, a hydrogen atom, a phenyl group, an alkyl group having a carbon number of at least 1 and no greater than 6, or an alkoxy group having a carbon number of at least 1 and no greater than 6. Q⁴⁷, Q⁴⁸, Q⁴⁹, and Q⁵⁰ each represent, independently of one another, a phenyl group, an alkyl group having a carbon number of at least 1 and no greater than 6, or an alkoxy group having a carbon number of at least 1 and no greater than 6. Furthermore, g₁ and g₂ each represent, independently of each other, an integer of at least 0 and no greater than 5. Also, g₃ and g₄ each represent, independently of each other, an integer of at least 0 and no greater than 4. Also, f represents 0 or 1.

When g₁ represents an integer of at least 2 and no greater than 5, plural chemical groups Q⁴⁷ may be the same as or different from one another. When g₂ represents an integer of at least 2 and no greater than 5, plural chemical groups Q⁴⁸ may be the same as or different from one another. When g₃ represents an integer of at least 2 and no greater than 4, plural chemical groups Q⁴⁹ may be the same as or different from one another. When g₄ represents an integer of at least 2 and no greater than 4, plural chemical groups Q⁵⁰ may be the same as or different from one another.

In general formula (14), Q⁴¹, Q⁴², Q⁴³, Q⁴⁴, Q⁴⁵, and Q⁴⁶ preferably each represent, independently of one another, a hydrogen atom or an alkyl group having a carbon number of at least 1 and no greater than 6. Preferably, g₁ and g₂ each represent 0. Preferably, g₃ and g₄ each represent 0. Preferably, f represents 0 or 1. The alkyl group having a carbon number of at least 1 and no greater than 6 represented by any of Q⁴¹, Q⁴², Q⁴³, Q⁴⁴, Q⁴⁵, and Q⁴⁶ is preferably an alkyl group having a carbon number of at least 1 and no greater than 3, and more preferably a methyl group or an ethyl group.

Preferable examples of the compound (14) include compounds represented by chemical formulas (14-HT1) and (14-HT2) shown below (also referred to below as compounds (14-HT1) and (14-HT2), respectively).

The following describes the compound (15). In general formula (15), Q⁵¹, Q⁵², Q⁵³, Q⁵⁴, Q⁵⁵, and Q⁵⁶ each represent, independently of one another, a phenyl group, an alkenyl group having a carbon number of at least 2 and no greater than 4 and optionally substituted by at least one phenyl group, an alkyl group having a carbon number of at least 1 and no greater than 6, or an alkoxy group having a carbon number of at least 1 and no greater than 6. Furthermore, h₃ and h₆ each represent, independently of each other, an integer of at least 0 and no greater than 4. Also, h₁, h₂, h₄, and h₅ each represent, independently of one another, an integer of at least 0 and no greater than 5.

When h₃ represents an integer of at least 2 and no greater than 4, plural chemical groups Q⁵³ may be the same as or different from one another. When h₆ represents an integer of at least 2 and no greater than 4, plural chemical groups Q⁵⁶ may be the same as or different from one another. When h₁ represents an integer of at least 2 and no greater than 5, plural chemical groups Q⁵¹ may be the same as or different from one another. When h₂ represents an integer of at least 2 and no greater than 5, plural chemical groups Q⁵² may be the same as or different from one another. When h₄ represents an integer of at least 2 and no greater than 5, plural chemical groups Q⁵⁴ may be the same as or different from one another. When h₅ represents an integer of at least 2 and no greater than 5, plural chemical groups Q⁵⁵ may be the same as or different from one another.

In general formula (15), Q⁵¹, Q⁵², Q⁵³, Q⁵⁴, Q⁵⁵, and Q⁵⁶ preferably each represent, independently of one another, an alkenyl group having a carbon number of at least 2 and no greater than 4 and optionally substituted by at least one phenyl group or an alkyl group having a carbon number of at least 1 and no greater than 6. Preferably, h₃ and h₆ each represent 0. Preferably, h₁, h₂, h₄, and h₅ each represent, independently of one another, an integer of at least 0 and no greater than 2. The alkenyl group having a carbon number of at least 2 and no greater than 4, optionally substituted by at least one phenyl group and represented by any of Q⁵¹, Q⁵², Q⁵³, Q⁵⁴, Q⁵⁵, and Q⁵⁶ is preferably an ethenyl group substituted by at least 1 and no greater than 3 phenyl groups, and more preferably a diphenylethenyl group. The alkyl group having a carbon number of at least 1 and no greater than 6 represented by any of Q⁵¹, Q⁵², Q⁵³, Q⁵⁴, Q⁵⁵, and Q⁵⁶ is preferably an alkyl group having a carbon number of at least 1 and no greater than 3, and more preferably a methyl group or an ethyl group.

Preferable examples of the compound (15) include compounds represented by chemical formulas (15-HT13), (15-HT14), and (15-HT15) shown below (also referred to below as compounds (15-HT13), (15-HT14), and (15-HT15), respectively).

The following describes the compound (16). In general formula (16), Q⁶¹, Q⁶², and Q⁶³ each represent, independently of one another, a phenyl group, an alkyl group having a carbon number of at least 1 and no greater than 6, or an alkoxy group having a carbon number of at least 1 and no greater than 6. Furthermore, f₁, f₂, and f₃ each represent, independently of one another, an integer of at least 0 and no greater than 5. Also, Q⁶⁴, Q⁶⁵, and Q⁶⁶ each represent, independently of one another, a hydrogen atom, a phenyl group optionally substituted by an alkyl group having a carbon number of at least 1 and no greater than 6, an alkyl group having a carbon number of at least 1 and no greater than 6, or an alkoxy group having a carbon number of at least 1 and no greater than 6. Also, f₄, f₅, and f₆ each represent, independently of one another, 0 or 1.

When f₁ represents an integer of at least 2 and no greater than 5, plural chemical groups Q⁶¹ may be the same as or different from one another. When f₂ represents an integer of at least 2 and no greater than 5, plural chemical groups Q⁶² may be the same as or different from one another. When f₃ represents an integer of at least 2 and no greater than 5, plural chemical groups Q⁶³ may be the same as or different from one another.

In general formula (16), Q⁶¹, Q⁶², and Q⁶³ preferably each represent, independently of one another, an alkyl group having a carbon number of at least 1 and no greater than 6. The alkyl group having a carbon number of at least 1 and no greater than 6 represented by any of Q⁶¹, Q⁶², and Q⁶³ is preferably an alkyl group having a carbon number of at least 1 and no greater than 3, and more preferably a methyl group. Preferably, f₁, f₂, and f₃ each represent, independently of one another, 0 or 1. Preferably, Q⁶⁴, Q⁶⁵, and Q⁶⁶ each represent a hydrogen atom. Preferably, f₄, f₅, and f₆ each represent 0.

A preferable example of the compound (16) is a compound represented by chemical formula (16-HT7) shown below (also referred to below as a compound (16-HT7)).

The following describes the compound (17). In general formula (17), Q⁷¹, Q⁷², Q⁷³, Q⁷⁴, Q⁷⁵, and Q⁷⁶ each represent, independently of one another, a halogen atom, an alkyl group having a carbon number of at least 1 and no greater than 6, an alkoxy group having a carbon number of at least 1 and no greater than 6, or an aryl group having a carbon number of at least 6 and no greater than 14. Furthermore, n₁, n₂, n₃, n₄, n₅, and n₆ each represent, independently of one another, an integer of at least 0 and no greater than 5. Also, x represents an integer of at least 1 and no greater than 3. Also, r and s each represent, independently of each other, 0 or 1.

When n₁ represents an integer of at least 2 and no greater than 5, plural chemical groups Q⁷¹ may be the same as or different from one another. When n₂ represents an integer of at least 2 and no greater than 5, plural chemical groups Q⁷² may be the same as or different from one another. When n₃ represents an integer of at least 2 and no greater than 5, plural chemical groups Q⁷³ may be the same as or different from one another. When n₄ represents an integer of at least 2 and no greater than 5, plural chemical groups Q⁷⁴ may be the same as or different from one another. When n₅ represents an integer of at least 2 and no greater than 5, plural chemical groups Q⁷⁵ may be the same as or different from one another. When n₆ represents an integer of at least 2 and no greater than 5, plural chemical groups Q⁷⁶ may be the same as or different from one another.

In general formula (17), Q⁷¹, Q⁷², Q⁷³, Q⁷⁴, Q⁷⁵, and Q⁷⁶ preferably each represent, independently of one another, an alkyl group having a carbon number of at least 1 and no greater than 6. Preferably, n₁, n₂, n₃, n₄, n₅, and n₆ each represent, independently of one another, 0 or 1. Preferably, x represents 2. Preferably, r and s each represent 0. The alkyl group having a carbon number of at least 1 and no greater than 6 represented by any of Q⁷¹, Q⁷², Q⁷³, Q⁷⁴, Q⁷⁵, and Q⁷⁶ is preferably an alkyl group having a carbon number of at least 1 and no greater than 3, and more preferably a methyl group.

A preferable example of the compound (17) is a compound represented by chemical formula (17-HT19) shown below (also referred to below as a compound (17-HT19)).

The following describes the compound (18). In general formula (18), Q⁸¹ and Q⁸² each represent, independently of each other, an alkyl group having a carbon number of at least 1 and no greater than 6 or an aryl group having a carbon number of at least 6 and no greater than 14, with the proviso that at least one of Q⁸¹ and Q⁸² represents an alkyl group having a carbon number of at least 1 and no greater than 6. Q⁸³ represents an alkyl group having a carbon number of at least 1 and no greater than 6, an alkoxy group having a carbon number of at least 1 and no greater than 6, an aralkyl group having a carbon number of at least 7 and no greater than 20, or an aryl group having a carbon number of at least 6 and no greater than 14. Furthermore, m represents an integer of at least 0 and no greater than 5. Also, p represents an integer of at least 0 and no greater than 2.

In general formula (18), Q⁸¹ and Q⁸² each represent an alkyl group having a carbon number of at least 1 and no greater than 6. Alternatively, one of Q⁸¹ and Q⁸² represents an alkyl group having a carbon number of at least 1 and no greater than 6 while the other represents an aryl group having a carbon number of at least 6 and no greater than 14.

In general formula (18), when m represents an integer of at least 2 and no greater than 5, plural chemical groups Q⁸³ present in the same aromatic ring may be the same as or different from one another.

In general formula (18), one of Q⁸¹ and Q⁸³ preferably represents an aryl group having a carbon number of at least 6 and no greater than 14. Preferably, m represents 0. Preferably, p represents 1. The alkyl group having a carbon number of at least 1 and no greater than 6 represented by any of Q⁸¹, Q⁸², and Q⁸³ is preferably an alkyl group having a carbon number of at least 1 and no greater than 3, and more preferably a methyl group. The aryl group having a carbon number of at least 6 and no greater than 14 represented by any of Q⁸¹, Q⁸², and Q⁸³ is preferably an aryl group having a carbon number of at least 6 and no greater than 10, and more preferably a phenyl group. The alkoxy group having a carbon number of at least 1 and no greater than 6 represented by Q⁸³ in general formula (18) is preferably an alkoxy group having a carbon number of at least 1 and no greater than 3. The aralkyl group having a carbon number of at least 7 and no greater than 20 represented by Q⁸³ is preferably an aralkyl group having a carbon number of at least 7 and no greater than 16.

A preferable example of the compound (18) is a compound represented by chemical formula (18-HT21) shown below (also referred to below as a compound (18-HT21)).

The photosensitive layer may contain only one or two or more of the compounds (11) to (18) as the hole transport material. For example, single use of the compound (12-HT3) or (12-HT10) may be possible. Alternatively, either the compound (12-HT3) or (12-HT10) may be used in combination with the compound (14-HT1). Note that the photosensitive layer may further contain a hole transport material other than the compounds (11) to (18) in addition to any of the compounds (11) to (18).

The content of the hole transport material is preferably at least 35% by mass relative to the mass of the photosensitive layer, and more preferably at least 40% by mass. The content of the hole transport material is preferably no greater than 65% by mass relative to the mass of the photosensitive layer, and more preferably no greater than 55% by mass. When the content of the hole transport material is at least 30% by mass relative to the mass of the photosensitive layer, an image defect resulting from exposure memory can be further effectively inhibited. Also, when the content of the hole transport material is no greater than 65% by mass relative to the mass of the photosensitive layer, an image defect resulting from exposure memory can be further effectively inhibited.

The ratio m_(HTM)/m_(ETM) of the mass m_(HTM) of the hole transport material to the mass m_(ETM) of the electron transport material is preferably at least 1.2, and more preferably at least 1.6. The ratio m_(HTM)/m_(ETM) of the mass m_(HTM) of the hole transport material to the mass m_(ETM) of the electron transport material is preferably no greater than 5.5, more preferably no greater than 4.0, and further preferably no greater than 3.0. When the ratio m_(HTM)/m_(ETM) is at least 1.2, an image defect resulting from exposure memory can be further effectively inhibited. Also, when the ratio m_(HTM)/m_(ETM) is no greater than 4.0, an image defect resulting from exposure memory can be further effectively inhibited. Note that in a situation in which two or more electron transport materials are contained in the photosensitive layer, the mass m_(ETM) of the electron transport material is a total mass of the two or more electron transport materials. Also, in a situation in which two or more hole transport materials are contained in the photosensitive layer, the mass m_(HTM) of the hole transport material is a total mass of the two or more hole transport materials.

An amount of the hole transport material contained in the photosensitive layer is preferably at least 10 parts by mass and no greater than 300 parts by mass relative to 100 parts by mass of the binder resin, more preferably at least 80 parts by mass and no greater than 250 parts by mass, and further preferably at least 120 parts by mass and no greater than 180 parts by mass.

(Electron Transport Material)

Examples of electron transport materials include quinone-based compounds, diimide-based compounds, hydrazone-based compounds, malononitrile-based compounds, thiopyran-based compounds, trinitrothioxanthone-based compounds, 3,4,5,7-tetranitro-9-fluorenone-based compounds, dinitroanthracene-based compounds, dinitroacridine-based compounds, tetracyanoethylene, 2,4,8-trinitrothioxanthone, dinitrobenzene, dinitroacridine, succinic anhydride, maleic anhydride, and dibromomaleic anhydride. Examples of quinone-based compounds include diphenoquinone-based compounds, azoquinone-based compounds, anthraquinone-based compounds, naphthoquinone-based compounds, nitroanthraquinone-based compounds, and dinitroanthraquinone-based compounds. Any one of the electron transport materials listed above may be used independently, or any two or more of the electron transport materials listed above may be used in combination.

Preferable examples of the electron transport materials listed above include compounds represented by general formulas (21), (22), and (23) shown below (also referred to below as compounds (21), (22), and (23), respectively).

In general formula (21), R¹¹ and R¹² each represent, independently of each other, an alkyl group having a carbon number of at least 1 and no greater than 6, an alkoxy group having a carbon number of at least 1 and no greater than 6, an aryl group having a carbon number of at least 6 and no greater than 14, or an aralkyl group having a carbon number of at least 7 and no greater than 20.

In general formula (21), R¹¹ and R¹² preferably each represent, independently of each other, an alkyl group having a carbon number of at least 1 and no greater than 6. The alkyl group having a carbon number of at least 1 and no greater than 6 represented by either or both R¹¹ and R¹² in general formula (21) is preferably an alkyl group having a carbon number of at least 1 and no greater than 5, and more preferably a 1,1-dimethylpropyl group.

Preferably, the compound (21) is a compound represented by chemical formula (ET1) shown below (also referred to below as a compound (ET1)).

In general formula (22), R²¹, R²², and R²³ each represent, independently of one another, a halogen atom, an alkyl group having a carbon number of at least 1 and no greater than 6, an alkoxy group having a carbon number of at least 1 and no greater than 6, an aryl group having a carbon number of at least 6 and no greater than 14 and optionally substituted by a halogen atom, an aralkyl group having a carbon number of at least 7 and no greater than 20, or a heterocyclic group having at least 5 members and no greater than 14 members.

In general formula (22), R²¹ and R²² preferably each represent, independently of each other, an alkyl group having a carbon number of at least 1 and no greater than 6. R²³ preferably represents an aryl group having a carbon number of at least 6 and no greater than 14 and optionally substituted by a halogen atom. The alkyl group having a carbon number of at least 1 and no greater than 6 represented by either or both R²¹ and R²² is preferably an alkyl group having a carbon number of at least 1 and no greater than 4, and more preferably a tert-butyl group. The aryl group having a carbon number of at least 6 and no greater than 14 represented by R²³ is preferably an aryl group having a carbon number of at least 6 and no greater than 10, and more preferably a phenyl group. The aryl group having a carbon number of at least 6 and no greater than 14 represented by R²³ may be substituted by a halogen atom. A halogen atom such as above is preferably a fluorine atom or a chlorine atom, and more preferably a chlorine atom. The number of halogen atoms by which an aryl group having a carbon number of at least 6 and no greater than 14 represented by R²³ is substituted is preferably at least 1 and no greater than 3, and more preferably 1.

Preferably, the compound (22) is a compound represented by chemical formula (ET2) shown below (also referred to below as a compound (ET2)).

In general formula (23), R³¹ and R³² each represent, independently of each other, a halogen atom, an amino group, an alkyl group having a carbon number of at least 1 and no greater than 6, an alkoxy group having a carbon number of at least 1 and no greater than 6, or an aryl group having a carbon number of at least 6 and no greater than 14 and optionally substituted by a substituent.

In general formula (23), R³¹ and R³² preferably each represent, independently of each other, an aryl group having a carbon number of at least 6 and no greater than 14 and optionally substituted by a substituent. The aryl group having a carbon number of at least 6 and no greater than 14 represented by either or both R³¹ and R³² is preferably an aryl group having a carbon number of at least 6 and no greater than 10, and more preferably a phenyl group. The aryl group having a carbon number of at least 6 and no greater than 14 represented by either or both R³¹ and R³² may be substituted by a substituent. Examples of substituents such as above include a halogen atom, a hydroxyl group, a nitro group, a cyano group, an alkyl group having a carbon number of at least 1 and no greater than 6, an alkoxy group having a carbon number of at least 1 and no greater than 6, and an aryl group having a carbon number of least 6 and no greater than 14. The substituent by which an aryl group having a carbon number of at least 6 and no greater than 14 represented by either or both R³¹ and R³² is substituted is preferably an alkyl group having a carbon number of at least 1 and no greater than 6, more preferably an alkyl group having a carbon number of at least 1 and no greater than 3, and further preferably a methyl group or an ethyl group. The number of substituents by which an aryl group having a carbon number of at least 6 and no greater than 14 represented by either or both R³¹ and R³² is substituted is preferably at least 1 and no greater than 3, more preferably at least 1 and no greater than 2, and further preferably 2.

Preferably, the compound (23) is a compound represented by chemical formula (ET3) shown below (also referred to below as a compound (ET3).

In order to further effectively inhibit an image defect resulting from exposure memory, the electron transport material is preferably the compound (21), and more preferably the compound (ET1).

The photosensitive layer may contain one of the compounds (21), (22) and (23) only as the electron transport material. Alternatively, the photosensitive layer may contain two or more of the compounds (21), (22) and (23) as the electron transport material. Furthermore, the photosensitive layer may further contain an electron transport material other than the compounds (21), (22), and (23) as the electron transport material in addition to any of the compounds (21), (22), and (23).

An amount of the electron transport material is preferably at least 20 parts by mass and no greater than 120 parts by mass relative to 100 parts by mass of the binder resin, more preferably at least 20 parts by mass and no greater than 100 parts by mass, further preferably at least 40 parts by mass and no greater than 90 parts by mass, and particularly preferably at least 60 parts by mass and no greater than 90 parts by mass.

In order to further effectively inhibit an image defect resulting from exposure memory, the mass m_(HTM) of the hole transport material, the mass m_(ETM) of the electron transport material, and a mass m_(R) of the binder resin preferably satisfy the following relational expression (A). [(m _(HTM) +m _(ETM))/m _(R)]>1.30  (A)

More preferably, (m_(HTM)+m_(ETM))/m_(R) is at least 1.50, and at least 2.00 is further preferable. Preferably, (m_(HTM)+m_(ETM))/m_(R) is no greater than 4.50. No greater than 3.50 is more preferable, and no greater than 2.50 is further preferable.

(Charge Generation Material)

No particular limitations are placed on the charge generating material other than being a charge generating material that can be used in photosensitive members. Examples of charge generating materials include phthalocyanine-based pigments, perylene-based pigments, bisazo pigments, tris-azo pigments, dithioketopyrrolopyrrole pigments, metal-free naphthalocyanine pigments, metal naphthalocyanine pigments, squaraine pigments, indigo pigments, azulenium pigments, cyanine pigments, powders of inorganic photoconductive materials (for example, selenium, selenium-tellurium, selenium-arsenic, cadmium sulfide, and amorphous silicon), pyrylium pigments, anthanthrone-based pigments, triphenylmethane-based pigments, threne-based pigments, toluidine-based pigments, pyrazoline-based pigments, and quinacridone-based pigments. Any one charge generating material may be used independently, or any two or more charge generating materials may be used in combination.

Examples of phthalocyanine-based pigments include metal-free phthalocyanines and metal phthalocyanines. Examples of metal phthalocyanines include titanyl phthalocyanine, hydroxygallium phthalocyanine, and chlorogallium phthalocyanine. Titanyl phthalocyanine is represented for example by chemical formula (CG1) shown below. Metal-free phthalocyanine is represented for example by chemical formula (CG2) shown below.

The phthalocyanine-based pigments may be crystalline or non-crystalline. No particular limitations are placed on crystal structure (for example, α-form, β-form, Y-form, V-form, or II-form) of the phthalocyanine-based pigments, and phthalocyanine-based pigments having various different crystal structures may be used. An example of crystalline metal-free phthalocyanines is metal-free phthalocyanine having an X-form crystal structure (also referred to below as X-form metal-free phthalocyanine). Examples of crystalline titanyl phthalocyanines include titanyl phthalocyanines having α-form, β-form, and Y-form crystal structures (also referred to below as α-form, β-form, and Y-form titanyl phthalocyanines).

In for example digital optical image forming apparatuses (for example, laser beam printers and facsimile machines each employing a semiconductor laser or the like as a light source), a photosensitive member that is sensitive to a wavelength range of 700 nm or longer is preferably used. As the charge generating material, a phthalocyanine-based pigment is preferable in terms of its high quantum yield in a wavelength range of 700 nm or longer. Metal-free phthalocyanine or titanyl phthalocyanine is more preferable. X-form metal-free phthalocyanine or Y-form titanyl phthalocyanine is further preferable. Y-form titanyl phthalocyanine is particularly preferable.

Y-form titanyl phthalocyanine exhibits a main peak for example at a Bragg angle (2θ±0.2°) of 27.2° in a CuKα characteristic X-ray diffraction spectrum. The term main peak refers to a peak having a highest or second highest intensity within a range of Bragg angles (2θ±0.2°) from 3° to 40° in a CuKα characteristic X-ray diffraction spectrum.

The following describes an example of a method for measuring a CuKα characteristic X-ray diffraction spectrum. A sample (titanyl phthalocyanine) is loaded into a sample holder of an X-ray diffraction spectrometer (for example, “RINT (registered Japanese trademark) 1100”, product of Rigaku Corporation), and an X-ray diffraction spectrum is measured using a Cu X-ray tube, a tube voltage of 40 kV, a tube current of 30 mA, and X-rays characteristic of CuKα having a wavelength of 1.542 Å. The measurement range (2θ) is for example from 3° to 40° (start angle: 3°, stop angle: 40°), and the scanning speed is for example 10°/minute.

For a photosensitive member in image forming apparatuses employing a short-wavelength laser light source (for example, a laser light source having a wavelength of at least 350 nm and no greater than 550 nm), an anthanthrone-based pigment is favorably used as the charge generating material.

An amount of the charge generating material is preferably at least 0.1 parts by mass and no greater than 50 parts by mass relative to 100 parts by mass of the binder resin contained in the photosensitive layer, more preferably at least 0.5 parts by mass and no greater than 30 parts by mass, and particularly preferably at least 0.5 parts by mass and no greater than 5 parts by mass.

(Binder Resin)

Examples of binder resins include thermoplastic resins, thermosetting resins, and photocurable resins. Examples of thermoplastic resins include polycarbonate resins, polyarylate resins, styrene-butadiene copolymers, styrene-acrylonitrile copolymers, styrene-maleic acid copolymers, acrylic acid polymers, styrene-acrylic acid copolymers, polyethylene resins, ethylene-vinyl acetate copolymers, chlorinated polyethylene resins, polyvinyl chloride resins, polypropylene resins, ionomer resins, vinyl chloride-vinyl acetate copolymers, alkyd resins, polyamide resins, urethane resins, polysulfone resins, diallyl phthalate resins, ketone resins, polyvinyl butyral resins, polyester resins, and polyether resins. Examples of thermosetting resins include silicone resins, epoxy resins, phenolic resins, urea resins, and melamine resins. Examples of photocurable resins include acrylic acid adducts of epoxy compounds and acrylic acid adducts of urethane compounds. Any one binder resin may be used independently, or any two or more binder resins may be used in combination.

The binder resin is preferably a polycarbonate resin including a repeating unit represented by general formula (31) shown below (also referred to below as a polycarbonate resin (31)).

In general formula (31), R⁴¹, R⁴², R⁴³, and R⁴⁴ each represent, independently of one another, a hydrogen atom, an alkyl group having a carbon number of at least 1 and no greater than 3 and optionally substituted by a halogen atom, or an aryl group having a carbon number of at least 6 and no greater than 14. R⁴³ and R⁴⁴ may be bonded together to represent a divalent group represented by general formula (X) shown below.

In general formula (X), t represents an integer of at least 1 and no greater than 3. Also, * represents a bond.

In general formula (31), the alkyl group having a carbon number of at least 1 and no greater than 3 represented by any of R⁴¹, R⁴², R⁴³, and R⁴⁴ is preferably a methyl group or an ethyl group. The alkyl group having a carbon number of at least 1 and no greater than 3 represented by any of R⁴¹, R⁴², R⁴³, and R⁴⁴ may be substituted by a halogen atom. The halogen atom by which an alkyl group having a carbon number of at least 1 and no greater than 3 is substituted is preferably a fluorine atom or a chlorine atom, and more preferably a fluorine atom. The number of halogen atoms by which an alkyl group having a carbon number of at least 1 and no greater than 3 is substituted is preferably at least 1 and no greater than 7, more preferably at least 1 and no greater than 5, and further preferably at least 1 and no greater than 3.

In general formula (31), the aryl group having a carbon number of at least 6 and no greater than 14 represented by any of R⁴¹, R⁴², R⁴³ and R⁴⁴ is preferably an aryl group having a carbon number of at least 6 and no greater than 10, and more preferably a phenyl group.

In general formula (X), t preferably represents 2.

In general formula (31), R⁴¹ and R⁴² preferably each represent, independently of each other, a hydrogen atom or an alkyl group having a carbon number of at least 1 and no greater than 3 and optionally substituted by a halogen atom. Preferably, R⁴³ and R⁴⁴ each represent, independently of each other, an alkyl group having a carbon number of at least 1 and no greater than 3, or are bonded together to represent a divalent group represented by general formula (X).

A preferable example of the polycarbonate resin (31) is a polycarbonate resin including a repeating unit represented by chemical formula (R1) shown below (also referred to below as a polycarbonate resin (R1)).

The polycarbonate resin (31) preferably has a viscosity average molecular weight of at least 25,000 and no greater than 60,000, and more preferably at least 35,000 and no greater than 53,000. When the polycarbonate resin (31) has a viscosity average molecular weight of at least 25,000, hardness of the photosensitive layer can be increased to an appropriate degree. When the polycarbonate resin (31) has a viscosity average molecular weight of no greater than 60,000, the polycarbonate resin (31) tends to readily dissolve in a solvent for photosensitive layer formation, thereby facilitating formation of the photosensitive layer.

The polycarbonate resin (31) may include the repeating unit represented by general formula (31) only as a repeating unit. Alternatively, the polycarbonate resin (31) may further include a repeating unit other than the repeating unit represented by general formula (31) in addition to the repeating unit represented by general formula (31). A ratio of the number of repeating units represented by general formula (31) to a total number of repeating units included in the polycarbonate resin (31) is preferably at least 0.80, more preferably at least 0.90, and particularly preferably 1.00.

The photosensitive layer may contain only one polycarbonate resin (31) as the binder resin. Alternatively, the photosensitive layer may contain two or more polycarbonate resins (31) as the binder resin. Furthermore, the photosensitive layer may further contain as the binder resin a binder resin other than the polycarbonate resin(s) (31) in addition to the polycarbonate resin(s) (31).

(Combination of Components)

Combinations (j-1) to (j-25) shown in Table 1 are each preferable as a combination of the hole transport material and the additive contained in the photosensitive layer. Furthermore, combinations (k-1) to (k-27) shown in Table 2 are each preferable as a combination of the hole transport material, the electron transport material, and the additive contained in the photosensitive layer. Note that “12-HT3/14-HT1”, “14-HT1/12-HT10”, and “AD1/AD3” shown under “Hole transport material” and “Additive” in Tables 1 and 2 indicate combinational use of the compounds (12-HT3) and (14-HT1), combinational use of the compounds (14-HT1) and (12-HT10), and combinational use of the compounds (AD1) and (AD3), respectively.

TABLE 1 Hole transport Combination material Additive j-1 14-HT1 AD1 j-2 14-HT2 AD1 j-3 12-HT3/14-HT1 AD1 j-4 12-HT4 AD1 j-5 12-HT5 AD1 j-6 12-HT6 AD1 j-7 16-HT7 AD1 j-8 11-HT8 AD1 j-9 11-HT9 AD1 j-10 14-HT1/12-HT10 AD1 j-11 12-HT11 AD1 j-12 12-HT12 AD1 j-13 15-HT13 AD1 j-14 15-HT14 AD1 j-15 15-HT15 AD1 j-16 13-HT16 AD1 j-17 13-HT17 AD1 j-18 12-HT18 AD1 j-19 17-HT19 AD1 j-20 14-HT1 AD2 j-21 14-HT1 AD3 j-22 14-HT1 AD1/AD3 j-23 14-HT1 AD4 j-24 14-HT1 AD5 j-25 18-HT21 AD1

TABLE 2 Hole transport Electron transport Combination material material Additive k-1 14-HT1 ET1 AD1 k-2 14-HT2 ET1 AD1 k-3 12-HT3/14-HT1 ET1 AD1 k-4 12-HT4 ET1 AD1 k-5 12-HT5 ET1 AD1 k-6 12-HT6 ET1 AD1 k-7 16-HT7 ET1 AD1 k-8 11-HT8 ET1 AD1 k-9 11-HT9 ET1 AD1 k-10 14-HT1/12-HT10 ET1 AD1 k-11 12-HT11 ET1 AD1 k-12 12-HT12 ET1 AD1 k-13 15-HT13 ET1 AD1 k-14 15-HT14 ET1 AD1 k-15 15-HT15 ET1 AD1 k-16 13-HT16 ET1 AD1 k-17 13-HT17 ET1 AD1 k-18 12-HT18 ET1 AD1 k-19 17-HT19 ET1 AD1 k-20 14-HT1 ET2 AD1 k-21 14-HT1 ET3 AD1 k-22 14-HT1 ET1 AD2 k-23 14-HT1 ET1 AD3 k-24 14-HT1 ET1 AD1/AD3 k-25 14-HT1 ET1 AD4 k-26 14-HT1 ET1 AD5 k-27 18-HT21 ET1 AD1

A preferable combination of the charge generating material, the hole transport material, and the additive contained in the photosensitive layer is a combination of X-form metal-free phthalocyanine and each component in any one of the combinations (j-1) to (j-22). A combination of Y-form titanyl phthalocyanine and each component of any one of the combinations (j-1) to (j-22) is also preferable.

A preferable combination of the charge generating material, the hole transport material, the additive, and the binder resin contained in the photosensitive layer is a combination of X-form metal-free phthalocyanine, the polycarbonate resin (R1), and each component in any one of the combinations (j-1) to (j-22). A combination of Y-form titanyl phthalocyanine, the polycarbonate resin (R1), and each component of any one of the combinations (j-1) to (j-22) is also preferable.

A preferable combination of the charge generating material, the hole transport material, the electron transport material, and the additive contained in the photosensitive layer is a combination of X-form metal-free phthalocyanine and each component in any one of the combinations (k-1) to (k-27). A combination of Y-form titanyl phthalocyanine and each component of any one of the combinations (k-1) to (k-27) is also preferable.

A preferable combination of the charge generating material, the hole transport material, the electron transport material, the additive, and the binder resin contained in the photosensitive layer is a combination of X-form metal-free phthalocyanine, the polycarbonate resin (R1), and each component in any one of the combinations (k-1) to (k-27). A combination of Y-form titanyl phthalocyanine, the polycarbonate resin (R1), and each component of any one of the combinations (k-1) to (k-27) is also preferable.

<Conductive Substrate>

No particular limitations are placed on the conductive substrate other than being a conductive substrate that can be used in photosensitive members. It is only required that at least a surface portion of the conductive substrate be made from a conductive material. An example of the conductive substrate is a conductive substrate made from a conductive material. Another example of the conductive substrate is a conductive substrate having a coating of a conductive material. Examples of conductive materials include aluminum, iron, copper, tin, platinum, silver, vanadium, molybdenum, chromium, cadmium, titanium, nickel, palladium, indium, stainless steel, and brass. Any one of the conductive materials listed above may be used independently, or any two or more of the conductive materials listed above may be used (for example, as an alloy) in combination. Among the conductive materials listed above, aluminum or an aluminum alloy is preferable in terms of favorable charge mobility from the photosensitive layer to the conductive substrate.

The shape of the conductive substrate is selected appropriately according to the configuration of an image forming apparatus to which the conductive substrate is applied. The conductive substrate is for example in a shape of a sheet or a drum. Furthermore, the thickness of the conductive substrate is appropriately selected according to the shape of the conductive substrate.

<Intermediate Layer>

The intermediate layer (undercoat layer) for example contains inorganic particles and a resin for intermediate layer use (intermediate layer resin). Presence of the intermediate layer is thought to enable smooth flow of current generated during exposure of the photosensitive member to light and inhibit increase in resistance, while also maintaining insulation to a sufficient degree to inhibit leakage current from occurring.

Examples of inorganic particles include particles of metals (for example, aluminum, iron, and copper), particles of metal oxides (for example, titanium oxide, alumina, zirconium oxide, tin oxide, and zinc oxide), and particles of non-metal oxides (for example, silica). Any one of the above-listed types of inorganic particles may be used independently, or any two or more of the above-listed types of inorganic particles may be used in combination.

No particular limitations are placed on the intermediate layer resin other than being a resin that can be used for intermediate layer formation. The intermediate layer may contain an additive. Examples of additives that may be contained in the intermediate layer are the same as the examples of the additives that may be contained in the photosensitive layer.

<Photosensitive Member Production Method>

The photosensitive member is produced for example by the following method. The photosensitive member is produced by applying an application liquid for photosensitive layer formation onto the conductive substrate and drying the application liquid thereon. The application liquid for photosensitive layer formation is prepared by dissolving or dispersing in a solvent the charge generating material, the electron transport material, the binder resin, the hole transport material, the additive, and a component added as needed (for example, the additional additive).

No particular limitations are placed on the solvent contained in the application liquid for photosensitive layer formation so long as each component contained in the application liquid can be dissolved or dispersed therein. Examples of the solvent include alcohols (for example, methanol, ethanol, isopropanol, and butanol), aliphatic hydrocarbons (for example, n-hexane, octane, and cyclohexane), aromatic hydrocarbons (for example, benzene, toluene, and xylene), halogenated hydrocarbons (for example, dichloromethane, dichloroethane, carbon tetrachloride, and chlorobenzene), ethers (for example, dimethyl ether, diethyl ether, tetrahydrofuran, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, and propylene glycol monomethyl ether), ketones (for example, acetone, methyl ethyl ketone, and cyclohexanone), esters (for example, ethyl acetate and methyl acetate), dimethyl formaldehyde, dimethyl formamide, and dimethyl sulfoxide. Any one of the solvents listed above may be used independently, or any two or more of the solvents listed above may be used in combination. In order to improve workability in photosensitive member production, a non-halogen solvent (solvent other than halogenated hydrocarbons) is preferably used as the solvent.

The application liquid for photosensitive layer formation is prepared by mixing the components and dispersing the components in the solvent. Mixing or dispersion can for example be performed using a bead mill, a roll mill, a ball mill, an attritor, a paint shaker, or an ultrasonic disperser.

The application liquid for photosensitive layer formation may for example further contain a surfactant in order to improve dispersibility of the components.

No particular limitations are placed on a method by which the application liquid for photosensitive layer formation is applied so long as the method enables uniform application of an application liquid onto a conductive substrate. Examples of application methods include blade coating, dip coating, spray coating, spin coating, and bar coating.

No particular limitations are placed on a method by which the application liquid for photosensitive layer formation is dried other than being a method for evaporating a solvent contained in an application liquid. One specific example of the method for drying involves thermal treatment (hot-air drying) using a high-temperature dryer or a reduced-pressure dryer. The temperature of thermal treatment is for example at least 40° C. and no greater than 150° C. A time for thermal treatment is for example at least 3 minutes and no greater than 120 minutes.

Note that the photosensitive member production method may further include either or both intermediate layer formation and protective layer formation as necessary. A known method is appropriately selected for each of the intermediate layer formation and the protective layer formation.

Second Embodiment: Image Forming Apparatus

The following describes an image forming apparatus according to a second embodiment. The image forming apparatus according to the second embodiment includes the photosensitive member according to the first embodiment. The following describes an aspect of the image forming apparatus according to the second embodiment using a tandem color image forming apparatus that adopts a direct transfer process with reference to FIG. 3.

An image forming apparatus 90 illustrated in FIG. 3 includes image forming units 40 a, 40 b, 40 c, and 40 d, a transfer belt 38, and a fixing section 36. In the following description, each of the image forming units 40 a, 40 b, 40 c, and 40 d may be referred to simply as an image forming unit 40 where it is not necessary to distinguish these units from one another.

Each of the image forming units 40 includes an image bearing member 30, a charger 42, a light exposure section 44, a developing section 46, and a transfer section 48. The image bearing member 30 is the photosensitive member 1 according to the first embodiment. The image bearing member 30 is disposed at a central position in the image forming unit 40. The image bearing member 30 is rotatable in an arrow direction (in a counterclockwise direction). The charger 42, the light exposure section 44, the developing section 46, and the transfer section 48 are disposed around the image bearing member 30 in the stated order from upstream in a rotational direction of the image bearing member 30 starting from the charger 42 as a reference. The image forming unit 40 may further include either or both a cleaner (not illustrated, specifically, a blade cleaner) and a static eliminator (not illustrated). Note that the image forming unit 40 may not include a cleaning blade. That is, the image forming apparatus 90 can adopt a process without blade cleaning.

Toner images in different colors (for example, four colors of black, cyan, magenta, and yellow) are consecutively superimposed on a recording medium M placed on the transfer belt 38 using the image forming units 40 a to 40 d.

The charger 42 charges a surface (specifically, a circumferential surface) of the image bearing member 30. The charger 42 has a positive charging polarity. That is, the charger 42 positively charges the surface of the image bearing member 30.

The charger 42 is a charging roller, for example. The charging roller charges the surface of the image bearing member 30 while in contact with the surface of the image bearing member 30. The image forming apparatus 90 adopts a contact charging process. An example of a charger that adopts the contact charging process other than the charging roller is a charging brush. Note that the charger may adopt a non-contact charging process. Examples of chargers that adopt the non-contact charging process include a corotron charger and a scorotron charger.

The light exposure section 44 exposes the charged surface of the image bearing member 30 to light. As a result of light exposure, an electrostatic latent image is formed on the surface of the image bearing member 30. The electrostatic latent image is formed based on image data input to the image forming apparatus 90.

The developing section 46 supplies toner to the surface of the image bearing member 30. Through toner supply, the developing section 46 develops the electrostatic latent image into a toner image. Thus, the image bearing member 30 bears the toner image. A developer used herein may be a one-component developer or a two-component developer. In a situation in which the developer is a one-component developer, the developing section 46 supplies toner, which is the one-component developer, to the electrostatic latent image formed on the surface of the image bearing member 30. In a situation in which the developer is a two-component developer, the developing section 46 supplies toner among the toner and a carrier included in the two-component developer to the electrostatic latent image formed on the surface of the image bearing member 30.

A time from light exposure of a specific location in the surface of the image bearing member 30 by the light exposure section 44 to development by the developing section 46 (also referred to below as a process time between exposure and development) is preferably no greater than 100 milliseconds. The process time between exposure and development specifically refers to a time from a start of exposure of the specific location in the surface of the image bearing member 30 to light emitted by the light exposure section 44 to a start of toner supply to the specific location by the developing section 46. The specific location in the surface of the image bearing member 30 is for example one point in a region of the circumferential surface of the image bearing member 30 on which light exposure is performed. The process time between exposure and development corresponds to a peripheral speed of the image bearing member 30.

Typically, when the process time between exposure and development is no greater than 100 milliseconds, the peripheral speed of an image bearing member is high and charges tend to remain in a photosensitive layer of an image bearing member. Therefore, an image defect resulting from exposure memory tends to occur. However, the image forming apparatus 90 includes the photosensitive member 1 according to the first embodiment as the image bearing member 30. As a result of use of the photosensitive member 1, an image defect resulting from exposure memory can be inhibited. Accordingly, even when the process time between exposure and development is no greater than 100 milliseconds, an image defect resulting from exposure memory can be inhibited through use of the image forming apparatus 90 including the photosensitive member 1 as the image bearing member 30.

The process time between exposure and development is preferably greater than 0 milliseconds and no greater than 100 milliseconds, more preferably at least 50 milliseconds and no greater than 90 milliseconds, and further preferably at least 65 milliseconds and no greater than 70 milliseconds.

The transfer belt 38 conveys the recording medium M to a location between the image bearing member 30 and the transfer section 48. The transfer belt 38 is an endless belt. The transfer belt 38 circulates in an arrow direction (in a clockwise direction).

The transfer section 48 transfers the toner image developed by the developing section 46 from the surface of the image bearing member 30 to a transfer target. The transfer target is the recording medium M. An example of the transfer section 48 is a transfer roller.

A region of the surface of the image bearing member 30 from which the toner image has been transferred to the recording medium M, which is the transfer target, by the transfer section 48 is re-charged by the charger 42 without static elimination performed. That is, the image forming apparatus 90 can adopt a so-called process without static elimination. Typically, charges tend to remain in a photosensitive layer of an image bearing member in an image forming apparatus that adopts the process without static elimination. Therefore, an image defect resulting from exposure memory tends to occur. However, the image forming apparatus 90 includes the photosensitive member 1 according to the first embodiment as the image bearing member 30. As a result of use of the photosensitive member 1, an image defect resulting from exposure memory can be inhibited. Accordingly, an image defect resulting from exposure memory can be inhibited even in the image forming apparatus 90 adopting the process without static elimination as long as the image forming apparatus 90 includes the photosensitive member 1 as the image bearing member 30.

The fixing section 36 applies heat and/or pressure to the toner images that have been transferred to the recording medium M by the transfer sections 48 and that have not been fixed yet. The fixing section 36 is for example a heating roller and/or a pressure roller. Application of heat and/or pressure to the toner images fixes the toner images to the recording medium M. Through the above, an image is formed on the recording medium M.

An example of the image forming apparatus has been described so far. However, the image forming apparatus is not limited to the above-described image forming apparatus 90. The above-described image forming apparatus 90 is a color image forming apparatus, but the image forming apparatus according to the present embodiment may be a monochrome image forming apparatus. In a configuration in which the image forming apparatus is a monochrome image forming apparatus, the image forming apparatus may include only one image forming unit, for example. The above-described image forming apparatus 90 is a tandem image forming apparatus, but the image forming apparatus according to the present embodiment may for example be a rotary image forming apparatus. The above-described image forming apparatus 90 adopts a direct transfer process, but the image forming apparatus according to the present embodiment may adopt for example an intermediate transfer process. In a configuration in which the image forming apparatus 90 adopts the intermediate transfer process, the transfer section includes a primary transfer section and a secondary transfer section and the transfer target includes a recording medium and a transfer belt.

Third Embodiment: Process Cartridge

The following describes a process cartridge according to a third embodiment. The process cartridge according to the third embodiment includes the photosensitive member according to the first embodiment. The following further describes an example of the process cartridge according to the third embodiment with reference again to FIG. 3. The process cartridge is a cartridge for image formation. The process cartridge corresponds to each of the image forming units 40 a to 40 d. The process cartridge includes the image bearing member 30. The image bearing member 30 is the photosensitive member 1 according to the first embodiment. The process cartridge may further include at least one selected from the group consisting of the charger 42, the light exposure section 44, the developing section 46, and the transfer section 48 in addition to the photosensitive member 1. The process cartridge may further include either or both a cleaner (not illustrated) and a static eliminator (not illustrated). The process cartridge is designed to be freely attachable to and detachable from the image forming apparatus 90. Accordingly, the process cartridge is easy to handle and can therefore be easily and quickly replaced, together with the photosensitive member 1, when sensitivity characteristics or the like of the photosensitive member 1 deteriorate. The process cartridge according to the third embodiment has been described with reference to FIG. 3.

EXAMPLES

The following provides more specific description of the present disclosure through use of Examples. However, the present disclosure is not in any way limited to the scope of Examples.

<Materials for Photosensitive Layer Formation>

The following electron transport materials, hole transport materials, charge generating materials, additives, and binder resin were prepared as materials for photosensitive layer formation for photosensitive members.

(Electron Transport Material)

The compounds (ET1) to (ET3) described in the first embodiment were prepared as the electron transport materials.

(Hole Transport Material)

The compounds (14-HT1), (14-HT2), (12-HT3), (12-HT4), (12-HT5), (12-HT6), (16-HT7), (11-HT8), (11-HT9), (12-HT10), (12-HT11), (12-HT12), (15-HT13), (15-HT14), (15-HT15), (13-HT16), (13-HT17), (12-HT18), (17-HT19), and (18-HT21) described in the first embodiment were prepared as the hole transport materials. A compound represented by chemical formula (HT20) shown below (also referred to below as a compound (HT20)) was also prepared as the hole transport material.

(Charge Generating Material)

Y-form titanyl phthalocyanine and X-form metal-free phthalocyanine were prepared as the charge generating materials. The Y-form titanyl phthalocyanine was a titanyl phthalocyanine having a Y-form crystal structure and represented by chemical formula (CG1) shown in the first embodiment (also referred to below as a compound (CG1)). The X-form metal-free phthalocyanine was a metal-free phthalocyanine having an X-form crystal structure and represented by chemical formula (CG2) shown in the first embodiment (also referred to below as a compound (CG2)).

(Additive)

The compounds (AD1) and (AD2), which each are a benzotriazole-based ultraviolet absorbing agent described in the first embodiment, and the compounds (AD3) to (AD5), which each are a hindered phenol-based antioxidant, were prepared as the additives. Specifically, the compounds (AD1) to (AD4) were “ADKSTAB (registered Japanese trademark) LA-36” (product of ADEKA Corporation), “ADKSTAB (registered Japanese trademark) LA-29” (product of ADEKA Corporation), “IRGANOX (registered Japanese trademark) 1010” (product of BASF Japan Ltd.), and “IRGANOX (registered Japanese trademark) 1076(product of BASF Japan Ltd.), respectively.

(Binder Resin)

The polycarbonate resin (R1) described in the first embodiment was prepared as the binder resin. The polycarbonate resin (R1) included the repeating unit represented by chemical formula (R1) only. The polycarbonate resin (R1) had a viscosity average molecular weight of 40,000.

<Photosensitive Member Production>

Photosensitive members (A-1) to (A-34) and (B-1) to (B-4) were produced with the materials for photosensitive layer formation.

(Production of Photosensitive Member (A-1))

A container was charged with 4 parts by mass of the compound (CG1) as the charge generating material, 150 parts by mass of the compound (14-HT1) as the hole transport material, 75 parts by mass of the compound (ET1) as the electron transport material, 5 parts by mass of the compound (AD1) as the additive, 100 parts by mass of the polycarbonate resin (R1) as the binder resin, and 800 parts by mass of tetrahydrofuran as a solvent. The container contents were mixed for 50 hours using a ball mill in order to disperse the materials in the solvent. Through the above, an application liquid for photosensitive layer formation was obtained. The application liquid for photosensitive layer formation was applied onto a conductive substrate (drum-shaped aluminum support, diameter: 30 mm, entire measuring apparatus length: 247.5 mm) by dip coating. After the application, the application liquid for photosensitive layer formation was dried at 120° C. for 60 minutes. Through the above, a photosensitive layer (film thickness: 28 μm) of a single layer was formed on the conductive substrate. The photosensitive member (A-1) was obtained as a result of the process described above.

(Production of Photosensitive Members (A-2) to (A-34) and (B-1) to (B-4))

The photosensitive members (A-2) to (A-34) and (B-1) to (B-4) were produced according to the same method as the method for producing the photosensitive member (A-1) in all aspects other than the following changes. The compound (CG1) was used as the charge generating material in production of the photosensitive member (A-1). By contrast, the charge generating materials shown in Tables 3 and 4 were used in production of the respective photosensitive members (A-2) to (A-34) and (B-1) to (B-4). In production of the photosensitive member (A-1), 150 parts by mass of the compound (14-HT1) was used as the hole transport material, 75 parts by mass of the compound (ET1) was used as the electron transport material, and the compound (AD1) was used as the additive. By contrast, the hole transport materials, the electron transport materials, and the additives of types and in amounts shown in Tables 3 and 4 were used in production of the respective photosensitive members (A-2) to (A-34) and (B-1) to (B-4).

<Measurement of Optical Response Time>

Optical response times were measured for the respective photosensitive members (A-1) to (A-34) and (B-1) to (B-4). The optical response times were measured in an environment at a temperature of 25° C. and a relative humidity of 50%.

The following describes a method for measuring an optical response time of the photosensitive member 1 with referent to FIG. 4. FIG. 4 illustrates a measuring apparatus 50 for measurement of an optical response time of the photosensitive member 1. The measuring apparatus 50 includes a charger 52, a light exposure device 54, a transparent probe 56, and a potential detector 58. A drum sensitivity test apparatus (product of Gen-Tech, Inc.) was used as the measuring apparatus 50. First, the photosensitive member 1 (specifically, any of the photosensitive members (A-1) to (A-34) and (B-1) to (B-4)) was attached to the measuring apparatus 50.

A surface 3 a of the photosensitive layer 3 of the photosensitive member 1 was charged to +800 V using the charger 52. Thus, the surface 3 a of the photosensitive layer 3 was charged to +800 V at a charging point A. The charging point A was located at a position where the charger 52 was in contact with the surface 3 a of the photosensitive layer 3.

The photosensitive member 1 was rotated in a direction from the charging point A to a light exposure point B (direction indicated by a solid arrow in FIG. 4) to move a point of the charged surface 3 a of the photosensitive layer 3 charged to +800 V to the light exposure point B. The light exposure point B was located at a position to be irradiated with pulse light. When the point of the charged surface 3 a of the photosensitive layer 3 charged to +800 V reached the light exposure point B, rotation of the photosensitive member 1 was stopped and the photosensitive member 1 was secured at the light exposure point B. The potential (surface potential) of the surface 3 a of the photosensitive layer 3 was measured with the photosensitive member 1 secured as above. The light exposure device 54 irradiated the light exposure point B of the charged surface 3 a of the photosensitive layer 3 with pulse light (wavelength: 780 nm, half-width: 40 microseconds). An optical intensity of the pulse light was set so that the surface potential of the photosensitive layer 3 became +200 V from +800 V when 400 milliseconds elapsed after irradiation of the surface 3 a of the photosensitive layer 3 charged to +800 V with the pulse light (more precisely, when 400 milliseconds elapsed from a time point when output of the pulse light with which the surface 3 a of the photosensitive layer 3 is irradiated exhibits peak output). Pulse light irradiation was performed one time. That is, irradiation with a single pulse of light was performed. A xenon flash lamp (“C4479”, product of Hamamatsu Photonics K.K.) was used as a light source of the light exposure device 54. Wavelength and optical intensity of the pulse light were adjusted using an optical filter (not illustrated). Technically, the surface 3 a of the photosensitive layer 3 was charged to a value slightly larger than +800 V by the charger 52. Next, when the surface potential of the photosensitive layer 3 dark decayed to +800 V through elapse of a specific time period, the surface 3 a of the photosensitive layer 3 was irradiated with the pulse light by the light exposure device 54.

The surface potential of the photosensitive layer 3 was measured using the transparent probe 56. The transparent probe 56 was disposed on an optical axis of the pulse light to allow the pulse light to transmit therethrough. A broken arrow from the light exposure device 54 to the photosensitive member 1 in FIG. 4 indicates the optical axis of the pulse light. A probe “3629A” (product of TREK, INC.) was used as the transparent probe 56.

The potential detector 58 was electrically connected to the transparent probe 56. The potential detector 58 obtained a surface potential of the photosensitive layer 3 each time the transparent probe 56 measured the surface potential of the photosensitive layer 3. Through the above, a surface potential decay curve for the photosensitive layer 3 was plotted. A time τ from a time of a start of the pulse light irradiation of the surface 3 a of the photosensitive layer 3 to a time when the surface potential of the photosensitive layer 3 decayed from +800 V to +400 V was determined from the plotted decay curve. The time τ determined as above was taken to be an optical response time. The method for measuring an optical response time of the photosensitive member 1 has been described with reference to FIG. 4. The measured optical response times of the photosensitive members are shown in Tables 3 and 4.

<Image Defect Resulting from Exposure Memory>

Whether or not an image defect resulting from exposure memory was inhibited was evaluated for each of the photosensitive members (A-1) to (A-34) and (B-1) to (B-4). Evaluation of an image defect resulting from exposure memory was performed in an environment at a temperature of 10° C. and a relative humidity of 15%.

The photosensitive member was attached to an evaluation apparatus. The evaluation apparatus used was a modified version of a color image forming apparatus (“FS-C5250DN”, product of KYOCERA Document Solutions Inc.). Modification in the modified version was removal of a cleaning blade and a static eliminator (specifically, a static elimination lamp) from the color image forming apparatus. That is, the evaluation apparatus included neither a static eliminator nor a cleaning blade that is a cleaner. The evaluation apparatus included a scorotron charger as a charger. The charge potential was set at +700 V. The peripheral speed of the photosensitive member was adjusted so that the process time between exposure and development was 72 milliseconds.

The following describes an evaluation image 70 employed in evaluation of an image defect resulting from exposure memory with reference to FIG. 5. FIG. 5 illustrates the evaluation image 70. The evaluation image 70 has a first region 72 and a second region 74. The first region 72 corresponds to a region of an image formed in the first turn of the image bearing member. The first region 72 includes a first image 76. The first image 76 is a donut-shaped solid image (image density: 100%). The solid image includes paired two concentric circles. The second region 74 corresponds to a region of an image formed in the second turn of the image bearing member. The second region 74 includes a second image 78. The second image 78 is a halftone image (image density: 40%) expanding over the entirety of the second region 74.

The following describes an image 80 with an image defect resulting from exposure memory with reference to FIG. 6. FIG. 6 illustrates the image 80 with an image defect resulting from exposure memory. The image 80 has the first region 72, the second region 74, the first image 76, and the second image 78 as in the above-described evaluation image 70. Once an image defect resulting from exposure memory occurs in printing of the evaluation image 70, a ghost image G appears in the second region 74 in addition to the second image 78 although only the second image 78 should have been printed. The ghost image G has an image density higher than that of the second image 78. The ghost image G is an image defect resulting from exposure memory and has a higher density than a designed image density due to reflection of a light exposure region corresponding to the first image 76 in the first region 72.

First, an image (print pattern image having a coverage of 4%) was printed on 3,000 recording mediums (A4-size paper) at intervals of 20 seconds using the evaluation apparatus. After the printing on 3,000 recording mediums, the evaluation image 70 illustrated in FIG. 5 was printed on one recording medium (A4-size paper). The printed evaluation image 70 was observed with an unaided eye to confirm presence or absence of an image defect resulting from exposure memory. Specifically, whether or not the ghost image G corresponding to the first image 76 appeared in the second region 74 of the evaluation image 70 was confirmed. Whether or not an image defect resulting from exposure memory could be inhibited was evaluated from results of observation on the evaluation image 70 based on the following criteria. Results of evaluation are shown in Tables 5 and 6. Note that evaluations A to C were each determined to be a passing mark.

(Evaluation Criteria for Image Defect Resulting from Exposure Memory)

Evaluation A: The ghost image G corresponding to the first image 76 was not observed.

Evaluation B: The ghost image G corresponding to the first image 76 was faintly observed.

Evaluation C: The ghost image G corresponding to the first image 76 was observed which involved no practical problem.

Evaluation D: The ghost image G corresponding to the first image 76 was apparently observed which involved a practical problem.

<Potential Stability>

Potential stability was evaluated for each of the photosensitive members (A-1) to (A-34) and (B-1) to (B-4). Evaluation of potential stability was performed in an environment at a temperature of 10° C. and a relative humidity of 15%.

First, the photosensitive member was attached to an evaluation apparatus. The evaluation apparatus used was the same as that used in evaluation of an image defect resulting from exposure memory. The charge potential was set at +700 V. The peripheral speed of the photosensitive member was adjusted so that the process time between exposure and development was 72 milliseconds.

Printing was performed on three sheets of blank paper, and a surface potential at a development point was measured three times in total in the printing. An average value of values measured in the three-time measurement was taken to be a surface potential V₀₁ (unit: +V) before test printing. Subsequently, the test printing was performed in which a print pattern (coverage: 1%) was printed on 10,000 recording mediums (A4-size paper) at intervals of 15 seconds. Directly after the test printing, printing was performed on three sheets of blank paper, and a surface potential at the development point was measured three times in total in the printing. An average value of values measured in the three-time measurement was taken to be a surface potential V₀₂ (unit: +V) after test printing. Potential stability was evaluated from a value (V₀₁−V₀₂) obtained by subtracting the surface potential V₀₂ after test printing from the surface potential V₀₁ before test printing based on the following criteria. Results of evaluation are shown in Tables 5 and 6. Note that evaluations A and B were each determined to be a passing mark.

(Evaluation Criteria for Potential Stability) V ₀₁ −V ₀₂<60 V  Evaluation A: 60 V≤V ₀₁ −V ₀₂<130 V  Evaluation B: 130 V≤V ₀₁ −V ₀₂  Evaluation C:

In Tables 3 and 4, “CGM”, “HTM”, “ETM”, “Part”, and “wt %” represent charge generating material, hole transport material, electron transport material, part by mass, and percentage by mass, respectively. Also, type “12-HT3/14-HT1” and amount “75/75” under “HTM” for the photosensitive member (A-7) shown in Table 3 indicate that the compounds (12-HT3) and (14-HT1) each in an amount of 75 parts by mass were contained as the hole transport material. Similarly, type “14-HT1/12-HT10” and amount “75/75” under “HTM” for the photosensitive member (A-14) shown in Table 3 indicate that the compounds (14-HT1) and (12-HT10) each in an amount of 75 parts by mass were contained as the hole transport material. Yet, type “AD1/AD3” and amount “2.5/2.5” under “Additive” for the photosensitive member (A-31) shown in Table 4 indicate that the compounds (AD1) and (AD3) each in an amount of 2.5 parts by mass were contained as the additive.

In Table 4, “-” under “Type” and “Amount” in “Additive” for the photosensitive member (B-4) indicates that no additive was contained.

In Tables 3 and 4, “Content” under “HTM” represents a content of the hole transport material relative to a mass of the photosensitive layer. The content of the hole transport material relative to the mass of the photosensitive layer was calculated using an calculation expression “content (unit: % by mass)=100×mass of hole transport material (unit: part by mass)/[mass of charge generating material (unit: part by mass)+mass of hole transport material (unit: part by mass)+mass of electron transport material (unit: part by mass)+mass of binder resin (unit: part by mass)]”.

In Tables 3 and 4, “Ratio m_(HTM)/m_(ETM)” represents a ratio of a mass m_(HTM) of the hole transport material to a mass m_(ETM) of the electron transport material. The ratio m_(HTM)/m_(ETM) was calculated using a calculation expression “ratio m_(HTM)/m_(ETM)=mass of hole transport material (unit: part by mass)/mass of electron transport material (unit: part by mass)”.

In Tables 3 and 4, “Ratio (m_(HmI)+m_(ETM))/m_(R)” represents a ratio of a total mass (mass m_(ETM)+mass m_(HTM)) of the electron transport material and the hole transport material to a mass m_(R) of the binder resin. The ratio (m_(HTM)+m_(ETM))/m_(R) was calculated using a calculation expression “ratio (m_(HTM)+m_(ETM))/m_(R)=[mass of hole transport material (unit: part by mass)+mass of electron transport material (unit: part by mass)]/mass of binder resin (unit: part by mass)”.

TABLE 3 Photosensitive layer Ratio Optical Photo- HTM ETM Additive Ratio (m_(HTM) + response sensitive Amount Content Amount Amount (m_(HTM)/ m_(ETM))/ time member CGM Type [part] [wt %] Type [part] Type [part] m_(ETM)) m_(R) [ms] Example 1 A-1 CG1 14-HT1  150 45 ET1 75 AD1 5 2.0 2.25 0.39 Example 2 A-2 CG1 14-HT1   90 37 ET1 45 AD1 5 2.0 1.35 0.76 Example 3 A-3 CG1 14-HT1  220 50 ET1 110 AD1 5 2.0 3.30 0.29 Example 4 A-4 CG1 14-HT1  280 63 ET1 55 AD1 5 5.1 3.35 0.84 Example 5 A-5 CG1 14-HT1  260 55 ET1 100 AD1 5 2.6 3.60 0.50 Example 6 A-6 CG1 14-HT2  150 45 ET1 75 AD1 5 2.0 2.25 0.29 Example 7 A-7 CG1  12-HT3/  75/75 45 ET1 75 AD1 5 2.0 2.25 0.36 14-HT1  Example 8 A-8 CG1 12-HT4  150 45 ET1 75 AD1 5 2.0 2.25 0.38 Example 9 A-9 CG1 12-HT5  150 45 ET1 75 AD1 5 2.0 2.25 0.30 Example 10  A-10 CG1 12-HT6  150 45 ET1 75 AD1 5 2.0 2.25 0.29 Example 11  A-11 CG1 16-HT7  150 45 ET1 75 AD1 5 2.0 2.25 0.39 Example 12  A-12 CG1 11-HT8  150 45 ET1 75 AD1 5 2.0 2.25 0.36 Example 13  A-13 CG1 11-HT9  150 45 ET1 75 AD1 5 2.0 2.25 0.52 Example 14  A-14 CG1  14-HT1/  75/75 45 ET1 75 AD1 5 2.0 2.25 0.34 12-HT10 Example 15  A-15 CG1 12-HT11 150 45 ET1 75 AD1 5 2.0 2.25 0.37 Example 16  A-16 CG1 12-HT12 150 45 ET1 75 AD1 5 2.0 2.25 0.39 Example 17  A-17 CG1 15-HT13 150 45 ET1 75 AD1 5 2.0 2.25 0.51 Example 18  A-18 CG1 15-HT14 150 45 ET1 75 AD1 5 2.0 2.25 0.56 Example 19  A-19 CG1 15-HT15 150 45 ET1 75 AD1 5 2.0 2.25 0.56 Example 20  A-20 CG1 13-HT16 150 45 ET1 75 AD1 5 2.0 2.25 0.65

TABLE 4 Photosensitive layer Ratio Optical Photo- HTM ETM Additive Ratio (m_(HTM) + response sensitive Amount Content Amount Amount (m_(HTM)/ m_(ETM))/ time member CGM Type [part] [wt %] Type [part] Type [part] m_(ETM)) m_(R) [ms] Example 21  A-21 CG1 13-HT17 150 45 ET1 75 AD1 5 2.0 2.25 0.63 Example 22  A-22 CG1 12-HT18 150 45 ET1 75 AD1 5 2.0 2.25 0.59 Example 23  A-23 CG1 17-HT19 150 45 ET1 75 AD1 5 2.0 2.25 0.29 Example 24  A-24 CG1 14-HT1  150 45 ET2 75 AD1 5 2.0 2.25 0.37 Example 25  A-25 CG1 14-HT1  150 45 ET3 75 AD1 5 2.0 2.25 0.41 Example 26  A-26 CG2 14-HT1  150 45 ET1 75 AD1 5 2.0 2.25 0.39 Example 27  A-27 CG1 14-HT1  150 45 ET1 75 AD1 1 2.0 2.25 0.37 Example 28  A-28 CG1 14-HT1  150 45 ET1 75 AD1 10 2.0 2.25 0.50 Example 29  A-29 CG1 14-HT1  150 45 ET1 75 AD2 5 2.0 2.25 0.42 Example 30  A-30 CG1 14-HT1  150 45 ET1 75 AD3 5 2.0 2.25 0.50 Example 31  A-31 CG1 14-HT1  150 45 ET1 75  AD1/ 2.5/ 2.0 2.25 0.43 AD3 2.5 Example 32  A-32 CG1 14-HT1  150 45 ET1 75 AD4 5 2.0 2.25 0.55 Example 33  A-33 CG1 14-HT1  150 45 ET1 75 AD5 5 2.0 2.25 0.62 Example 34  A-34 CG1 18-HT21 150 45 ET1 75 AD1 5 2.0 2.25 0.27 Comparative B-1 CG1 14-HT1  50 45 ET1 75 AD1 5 0.7 1.20 93.00 Example 1 Comparative B-2 CG1 14-HT1  70 45 ET1 50 AD1 5 1.4 1.20 2.90 Example 2 Comparative B-3 CG1 HT-20  150 45 ET1 75 AD1 5 2.0 2.25 3.90 Example 3 Comparative B-4 CG1 14-HT1  150 45 ET1 75 — — 2.0 2.25 0.33 Example 4

TABLE 5 Inhibition of Potential stability Photosensitive exposure V₀₁-V₀₂ member memory [+V] Evaluation Example 1 A-1 A 51 A Example 2 A-2 C 44 A Example 3 A-3 A 53 A Example 4 A-4 A 55 A Example 5 A-5 C 62 B Example 6 A-6 A 45 A Example 7 A-7 A 40 A Example 8 A-8 A 43 A Example 9 A-9 A 42 A Example 10 A-10 A 45 A Example 11 A-11 A 48 A Example 12 A-12 B 45 A Example 13 A-13 C 51 A Example 14 A-14 A 55 A Example 15 A-15 A 53 A Example 16 A-16 A 55 A Example 17 A-17 B 68 B Example 18 A-18 C 60 B Example 19 A-19 C 64 B Example 20 A-20 C 60 B Example 21 A-21 C 57 A Example 22 A-22 C 45 A Example 23 A-23 A 69 B Example 24 A-24 A 50 A Example 25 A-25 B 55 A Example 26 A-26 A 40 A Example 27 A-27 A 80 B Example 28 A-28 C 42 A Example 29 A-29 A 53 A Example 30 A-30 C 45 A Example 31 A-31 A 37 A Example 32 A-32 C 41 A Example 33 A-33 C 36 A Example 34 A-34 A 40 A

TABLE 6 Inhibition of Potential stability Photosensitive exposure V₀₁-V₀₂ member memory [+V] Evaluation Comparative B-1 D 108 B Example 1 Comparative B-2 D  87 B Example 2 Comparative B-3 D 134 C Example 3 Comparative B-4 B 173 C Example 4

Each of the photosensitive members (A-1) to (A-34) included a conductive substrate and a photosensitive layer that was a single layer. The photosensitive layer contained a charge generating material, a hole transport material, an electron transport material, an additive, and a binder resin. An optical response time was at least 0.05 milliseconds and no greater than 0.85 milliseconds. The photosensitive layer of each of the photosensitive members (A-1) to (A-34) contained at least one of an ultraviolet absorbing agent and an antioxidant as the additive. As a result, each of the photosensitive members (A-1) to (A-34) was evaluated as any one of A to C in evaluation of inhibition of an image defect resulting from exposure memory and evaluated as A or B in evaluation of potential stability. This means that each photosensitive member made passing marks in evaluation of inhibition of an image defect resulting from exposure memory and evaluation of potential stability, as shown in Table 5. That is, an image defect resulting from exposure memory could be inhibited and excellent potential stability was achieved with use of any of the photosensitive members (A-1) to (A-34).

By contrast, respective optical response times of the photosensitive members (B-1) to (B-3) exceeded 0.85 milliseconds. As a result, each of the photosensitive members (B-1) to (B-3) was evaluated as D in evaluation of inhibition of an image defect resulting from exposure memory, as shown in Table 6. That is, an image defect resulting from exposure memory was insufficiently inhibited with use of any of the photosensitive members (B-1) to (B-3). Furthermore, the photosensitive member (B-3) was evaluated as C in evolution of potential stability. That is, potential stability was insufficient in the photosensitive member (B-3).

The photosensitive member (B-4) included a photosensitive layer that contained no additive. As a result, the photosensitive member (B-4) was evaluated as C in evaluation of potential stability, as shown in Table 6. That is, potential stability was insufficient in the photosensitive member (B-4).

It was indicated from the above that an image defect resulting from exposure memory could be inhibited and excellent potential stability could be achieved when the photosensitive member according to the present disclosure was used. Furthermore, it was also indicated that an image defect resulting from exposure memory could be inhibited and excellent potential stability could be achieved when the process cartridge or the image forming apparatus according to the present disclosure were used. 

What is claimed is:
 1. An electrophotographic photosensitive member comprising a conductive substrate and a photosensitive layer of a single layer, wherein the photosensitive layer contains a charge generating material, a hole transport material, an electron transport material, an additive, and a binder resin, an optical response time is at least 0.05 milliseconds and no greater than 0.85 milliseconds, the optical response time is a time from irradiation to decay, the irradiation being a time of a start of irradiation of a surface of the photosensitive layer charged to +800 V with pulse light having a wavelength of 780 nm, the decay being a time when a surface potential of the photosensitive layer decays from +800 V to +400 V, an optical intensity of the pulse light is set so that the surface potential of the photosensitive layer becomes+200 V from +800 V when 400 milliseconds elapse after the irradiation of the surface of the photosensitive layer charged to +800 V with the pulse light, the additive includes a compound represented by a general formula (1), and a mass m_(HTM) of the hole transport material, a mass m_(ETM) of the electron transport material, and a mass m_(R) of the binder resin satisfy a relational expression (A) shown below: [(m _(HTM) +m _(ETM))/m _(R)]>1.30  (A),

where in the general formula (1), R¹ represents a halogen atom or an alkyl group having a carbon number of at least 1 and no greater than 6 and substituted by a halogen atom, R² represents an alkyl group having a carbon number of at least 1 and no greater than 10, an aralkyl group having a carbon number of at least 7 and no greater than 20, or an aryl group having a carbon number of at least 6 and no greater than 22, n and m each represent, independently of each other, an integer of at least 0 and no greater than 4, when n represents an integer of at least 2 and no greater than 4, plural chemical groups R¹ may be the same as or different from one another, and when m represents an integer of at least 2 and no greater than 4, plural chemical groups R² may be the same as or different from one another.
 2. The electrophotographic photosensitive member according to claim 1, wherein the compound represented by the general formula (1) includes a compound represented by a chemical formula (AD1) or (AD2) shown below,


3. The electrophotographic photosensitive member according to claim 1, wherein a ratio m_(HTM)/m_(ETM) of a mass m_(HTM) of the hole transport material to a mass m_(ETM) of the electron transport material is at least 1.2 and no greater than 4.0.
 4. The electrophotographic photosensitive member according to claim 1, wherein a content of the hole transport material is at least 35% by mass and no greater than 65% by mass relative to a mass of the photosensitive layer.
 5. The electrophotographic photosensitive member according to claim 1, wherein a content of the compound represented by the general formula (1) is at least 0.1 parts by mass and no greater than 15 parts by mass relative to 100 parts by mass of the binder resin.
 6. The electrophotographic photosensitive member according to claim 1, wherein the optical response time is at least 0.05 milliseconds and no greater than 0.60 milliseconds.
 7. The electrophotographic photosensitive member according to claim 1, wherein the hole transport material includes a compound represented by a general formula (11), (12), (13), (14), (15), (16), (17), or (18) shown below,

where in the general formula (11), Q¹, Q², Q³, and Q⁴ each represent, independently of one another, an alkyl group having a carbon number of at least 1 and no greater than 6, b₁, b₂, b₃, and b₄ each represent, independently of one another, an integer of at least 0 and no greater than 5, and b₅ represents 0 or 1, in the general formula (12), Q²¹ and Q²⁸ each represent, independently of each other, a hydrogen atom, a phenyl group optionally substituted by an alkyl group having a carbon number of at least 1 and no greater than 6, an alkyl group having a carbon number of at least 1 and no greater than 6, or an alkoxy group having a carbon number of at least 1 and no greater than 6, Q²² and Q²⁹ each represent, independently of each other, a phenyl group, an alkyl group having a carbon number of at least 1 and no greater than 6, or an alkoxy group having a carbon number of at least 1 and no greater than 6, Q²³, Q²⁴, Q²⁵, Q²⁶, and Q²⁷ each represent, independently of one another, a phenyl group, a hydrogen atom, an alkyl group having a carbon number of at least 1 and no greater than 6, or an alkoxy group having a carbon number of at least 1 and no greater than 6, two adjacent chemical groups among Q²³, Q²⁴, Q²⁵, Q²⁶ and Q²⁷ may be bonded together to form a ring, d₁ and d₂ each represent, independently of each other, an integer of at least 0 and no greater than 2, and d₃ and d₄ each represent, independently of each other, an integer of at least 0 and no greater than 5, in the general formula (13), Q³¹, Q³², Q³³, and Q³⁴ each represent, independently of one another, an alkyl group having a carbon number of at least 1 and no greater than 6 or an alkoxy group having a carbon number of at least 1 and no greater than 6, e₁, e₂, e₃, and e₄ each represent, independently of one another, an integer of at least 0 and no greater than 5, and e₅ represents 2 or 3, in the general formula (14), Q⁴¹, Q⁴², Q⁴³, Q⁴⁴, Q⁴⁵, and Q⁴⁶ each represent, independently of one another, a hydrogen atom, a phenyl group, an alkyl group having a carbon number of at least 1 and no greater than 6, or an alkoxy group having a carbon number of at least 1 and no greater than 6, Q⁴⁷, Q⁴⁸, Q⁴⁹, and Q⁵⁰ each represent, independently of one another, a phenyl group, an alkyl group having a carbon number of at least 1 and no greater than 6, or an alkoxy group having a carbon number of at least 1 and no greater than 6, g₁ and g₂ each represent, independently of each other, an integer of at least 0 and no greater than 5, g₃ and g₄ each represent, independently of each other, an integer of at least 0 and no greater than 4, and f represents 0 or 1, in the general formula (15), Q⁵¹, Q⁵², Q⁵³, Q⁵⁴, Q⁵⁵, and Q⁵⁶ each represent, independently of one another, a phenyl group, an alkenyl group having a carbon number of at least 2 and no greater than 4 and optionally substituted by at least one phenyl group, an alkyl group having a carbon number of at least 1 and no greater than 6, or an alkoxy group having a carbon number of at least 1 and no greater than 6, h₃ and h₆ each represent, independently of each other, an integer of at least 0 and no greater than 4, and h₁, h₂, h₄, and h₅ each represent, independently of one another, an integer of at least 0 and no greater than 5, in the general formula (16), Q⁶¹, Q⁶², and Q⁶³ each represent, independently of one another, a phenyl group, an alkyl group having a carbon number of at least 1 and no greater than 6, or an alkoxy group having a carbon number of at least 1 and no greater than 6, f₁, f₂, and f₃ each represent, independently of one another, an integer of at least 0 and no greater than 5, Q⁶⁴, Q⁶⁵, and Q⁶⁶ each represent, independently of one another, a hydrogen atom, a phenyl group optionally substituted by an alkyl group having a carbon number of at least 1 and no greater than 6, an alkyl group having a carbon number of at least 1 and no greater than 6, or an alkoxy group having a carbon number of at least 1 and no greater than 6, and f₄, f₅, and f₆ each represent, independently of one another, 0 or 1, in the general formula (17), Q⁷¹, Q⁷², Q⁷³, Q⁷⁴, Q⁷⁵, and Q⁷⁶ each represent, independently of one another, a halogen atom, an alkyl group having a carbon number of at least 1 and no greater than 6, an alkoxy group having a carbon number of at least 1 and no greater than 6, or an aryl group having a carbon number of at least 6 and no greater than 14, n₁, n₂, n₃, n₄, n₅, and n₆ each represent, independently of one another, an integer of at least 0 and no greater than 5, x represents an integer of at least 1 and no greater than 3, and r and s each represent, independently of each other, 0 or 1, and in the general formula (18), Q⁸¹ and Q⁸² each represent, independently of each other, an alkyl group having a carbon number of at least 1 and no greater than 6 or an aryl group having a carbon number of at least 6 and no greater than 14, with a proviso that at least one of Q⁸¹ and Q⁸² represents an alkyl group having a carbon number of at least 1 and no greater than 6, Q⁸³ represents an alkyl group having a carbon number of at least 1 and no greater than 6, an alkoxy group having a carbon number of at least 1 and no greater than 6, an aralkyl group having a carbon number of at least 7 and no greater than 20, or an aryl group having a carbon number of at least 6 and no greater than 14, m represents an integer of at least 0 and no greater than 5, and p represents an integer of at least 0 and no greater than
 2. 8. The electrophotographic photosensitive member according to claim 7, wherein in the general formula (11), Q¹, Q², Q³, and Q⁴ each represent, independently of one another, an alkyl group having a carbon number of at least 1 and no greater than 3, b¹, b2, b3, and b4 each represent, independently of one another, 0 or 1, and b₅ represents 0 or 1, in the general formula (12), Q²¹ and Q²⁸ each represent, independently of each other, a hydrogen atom or a phenyl group optionally substituted by an alkyl group having a carbon number of at least 1 and no greater than 6, Q²² and Q²⁹ each represent, independently of each other, an alkyl group having a carbon number of at least 1 and no greater than 6, Q²³, Q²⁴, Q²⁵, Q²⁶, and Q²⁷ each represent, independently of one another, a hydrogen atom, an alkyl group having a carbon number of at least 1 and no greater than 6, or an alkoxy group having a carbon number of at least 1 and no greater than 6, two adjacent chemical groups among Q²³, Q²⁴, Q²⁵, Q²⁶ and Q²⁷ may be bonded together to form a cycloalkane having a carbon number of at least 5 and no greater than 7, d₁ and d₂ each represent, independently of each other, an integer of at least 0 and no greater than 2, and d₃ and d₄ each represent, independently of each other, 0 or 1, in the general formula (13), Q³¹, Q³², Q³³, and Q³⁴ each represent, independently of one another, an alkyl group having a carbon number of at least 1 and no greater than 6, e₁, e₂, e₃, and e₄ each represent, independently of one another, 0 or 1, and e₅ represents 2 or 3, in the general formula (14), Q⁴¹, Q⁴², Q⁴³, Q⁴⁴, Q⁴⁵, and Q⁴⁶ each represent, independently of one another, a hydrogen atom or an alkyl group having a carbon number of at least 1 and no greater than 6, g₁ and g₂ each represent 0, g₃ and g₄ each represent 0, and f represents 0 or 1, in the general formula (15), Q⁵¹, Q⁵², Q⁵³, Q⁵⁴, Q⁵⁵, and Q⁵⁶ each represent, independently of one another, an alkenyl group having a carbon number of at least 2 and no greater than 4 and optionally substituted by at least one phenyl group, or an alkyl group having a carbon number of at least 1 and no greater than 6, h₃ and h₆ each represent 0, and h₁, h₂, h₄, and h₅ each represent, independently of one another, an integer of at least 0 and no greater than 2, in the general formula (16), Q⁶¹, Q⁶², and Q⁶³ each represent, independently of one another, an alkyl group having a carbon number of at least 1 and no greater than 6, f₁, f₂, and f₃ each represent, independently of one another, 0 or 1, Q⁶⁴, Q⁶⁵, and Q⁶⁶ each represent a hydrogen atom, and f₄, f₅, and f₆ each represent 0, in the general formula (17), Q⁷¹, Q⁷², Q⁷³, Q⁷⁴, Q⁷⁵, and Q⁷⁶ each represent, independently of one another, an alkyl group having a carbon number of at least 1 and no greater than 6, n₁, n₂, n₃, n₄, n₅, and n₆ each represent, independently of one another, 0 or 1, x represents 2, and r and s each represent 0, and in the general formula (18), both Q⁸¹ and Q⁸² represent an alkyl group having a carbon number of at least 1 and no greater than 6, or one of Q⁸¹ and Q⁸² represents an alkyl group having a carbon number of at least 1 and no greater than 6 and the other represents an aryl group having a carbon number of at least 6 and no greater than 14, m represents 0, and p represents
 1. 9. The electrophotographic photosensitive member according to claim 1, wherein the hole transport material includes a compound represented by a chemical formula (14-HT1), (14-HT2), (12-HT3), (12-HT4), (12-HT5), (12-HT6), (16-HT7), (11-HT8), (11-HT9), (12-HT10), (12-HT11), (12-HT12), (15-HT13), (15-HT14), (15-HT15), (13-HT16), (13-HT17), (12-HT18), (17-HT19), or (18-HT21) shown below,


10. The electrophotographic photosensitive member according to claim 1, wherein the electron transport material includes a compound represented by a general formula (21), (22), or (23) shown below,

where in the general formula (21), R¹¹ and R¹² each represent, independently of each other, an alkyl group having a carbon number of at least 1 and no greater than 6, an alkoxy group having a carbon number of at least 1 and no greater than 6, an aryl group having a carbon number of at least 6 and no greater than 14, or an aralkyl group having a carbon number of at least 7 and no greater than 20, in the general formula (22), R²¹, R²², and R²³ each represent, independently of one another, a halogen atom, an alkyl group having a carbon number of at least 1 and no greater than 6, an alkoxy group having a carbon number of at least 1 and no greater than 6, an aryl group having a carbon number of at least 6 and no greater than 14 and optionally substituted by a halogen atom, an aralkyl group having a carbon number of at least 7 and no greater than 20, or a heterocyclic group having at least 5 members and no greater than 14 members, and in the general formula (23), R³¹ and R³² each represent, independently of each other, a halogen atom, an amino group, an alkyl group having a carbon number of at least 1 and no greater than 6, an alkoxy group having a carbon number of at least 1 and no greater than 6, or an aryl group having a carbon number of at least 6 and no greater than 14 and optionally substituted by a substituent.
 11. The electrophotographic photosensitive member according to claim 1, wherein the electron transport material includes a compound represented by a chemical formula (ET1), (ET2), or (ET3) shown below,


12. A process cartridge comprising the electrophotographic photosensitive member according to claim
 1. 13. An image forming apparatus comprising: an image bearing member; a charger configured to charge a surface of the image bearing member; a light exposure section configured to expose the charged surface of the image bearing member to light to form an electrostatic latent image on the surface of the image bearing member; a developing section configured to develop the electrostatic latent image into a toner image; and a transfer section configured to transfer the toner image from the image bearing member to a transfer target, wherein the charger positively charges the surface of the image bearing member, and the image bearing member is the electrophotographic photosensitive member according to claim
 1. 14. The electrophotographic photosensitive member according to claim 1, wherein a content of the compound represented by the general formula (1) is at least 3 parts by mass and no greater than 7 parts by mass relative to 100 parts by mass of the binder resin, and the relational expression (A) is a relational expression (A1) shown below, 2.00≤[(m _(HTM) +m _(ETM))/m _(R)]≤3.50  (A1).
 15. The electrophotographic photosensitive member according to claim 1, wherein the hole transport material includes a compound represented by chemical formula (18-HT21) shown below,


16. The electrophotographic photosensitive member according to claim 1, wherein the compound represented by the general formula (1) is a compound represented by a chemical formula (AD2) shown below,


17. The electrophotographic photosensitive member according to claim 1, wherein the additive includes no antioxidant.
 18. The electrophotographic photosensitive member according to claim 1, wherein the additive includes only the compound represented by the general formula (1).
 19. The electrophotographic photosensitive member according to claim 1, wherein the hole transport material includes a compound represented by a chemical formula (14-HT1), (14-HT2), (12-HT4), (12-HT5), (12-HT6), (16-HT7), (11-HT8), (12-HT10), (12-HT11), (12-HT12), (15-HT13), (17-HT19), or (18-HT21), a content of the compound represented by the general formula (1) is at least 0.1 parts by mass and no greater than 7 parts by mass relative to 100 parts by mass of the binder resin, and the relational expression (A) is a relational expression (A1) shown below, 2.00≤[(m _(HTM) +m _(ETM))/m _(R)]≤3.50  (A1) 